Elements of Electron Microscopy Designing Laboratory Course: Examples and Applications

Abstract

This chapter provides guidance on designing laboratory practices for material characterization using electron microscopy, with a focus on the advantages of using backscattered electrons (BSE), secondary electrons (SE), and energy-dispersive spectroscopy (EDS). The approach includes insights into using other microscopy techniques such as atomic force microscopy (AFM), ellipsometry, and optical profilometry as complementary methods to validate results from electron microscopy. Examples of applications include eutectic alloys, thermal oxides, and nanoparticles in various industries. Successful syllabuses for undergraduate and graduate courses are illustrated, and the laboratory teachings’ results were presented at a conference and published in peer-reviewed journals.

1. Introduction

The design and teaching implementation of material characterization laboratory practicums present a challenge to many teaching professionals. There are many variables in that task:

1. scientific instrumentation availability

2. technical difficulty of the lab (graduate or undergraduate level)

3. number of students per class

4. goals or what we want students to accomplish by the end of the quarter or semester

5. desired assistance or how many student assistants one can get.

The design thinking approach shared in this chapter is based on my experience developing and teaching both graduate and undergraduate level courses with labs at Santa Clara University, CA, USA. The inspiration for syllabus development came from a couple of sources: “Elements of X-ray diffraction” by Cullity and Stock [1] and “The design of everyday things” by Norman [2]. Design thinking should not be an afterthought, but rather a guiding principle for syllabus development. Conceptual understanding is just as important as attention to technical details. Our experience and knowledge of product management have been applied to the development of new laboratory practicums. Examples of syllabuses taught along with students reported results are shared below. The goal of this chapter is to be a useful practical guide for teaching technical labs with electron microscopes.

The structure of the chapter follows the flow of my materials characterization lecture. We start with the assumption we have a scanning electron microscope (SEM) and atomic force microscope (AFM) at our disposal, Section 2 and Section 3 respectively. The SEM and the AFM are two fundamental pillars for teaching materials, science and nanotechnology [3, 4]. The core idea for the lab teaching is complementary characterization, verification, of the results obtained by one technique with an independent measurement by a second method. SEM and AFM pair very nicely in the micro-nano range. SEM is well-established 2D or XY imaging technique [5, 6], while only AFM is truly 3D [7, 8, 9]. One of the main advantages of SEM besides million times magnification is the benefit of large depth of field, see Getty images [10] of insects. The perception of the three dimensions is most remarkable. AFM, however, provides direct height measurement and 3D visualization from atomic scale as it can be seen in IBM images [11] of atoms and molecules as well as pioneering work toward nanomanipulation. Both AFM and scanning tunneling microscopy (STM) are the members of a larger family named scanning probe microscopy (SPM) [3, 4, 5, 8, 9]. SPM generally stands for a technique where a probe, a stylus, is being used to measure variations of topography while raster scanning.

The core of a student’s project is in dual measurements. For example, first practice XY dimensions measurements with SEM, confirm with AFM and then determine Z height with AFM. The choice of samples can range from mechanically polished alloy to thermally grown oxides to nanoparticles, see Sections 7 and 8 of this chapter. XYZ measurements project facilitates the learning of SEM and AFM in the topography modes. The ultimate goal of the lab is to learn how to run the microscopes or how to acquire and analyze the data, is entirely up to the teaching instructor, the idea of dual measurements is central for my syllabuses. In addition, we use an approach of “station rotation” that has proven to be beneficial by allowing students to gain more hand-on experience during the lab and reduce number of students per group.

The idea of dual measurements can be expanded into various operating modes of both SEM and AFM. For example, elemental composition mapping or EDX imaging is a standard mode in SEM [7, 8] that can be complemented by AFM phase imaging or frictional mode. Lateral force mode (LFM or friction) and phase mode are usually acquired simultaneously with topography AFM. The standard materials sensing properties modes, although, are electrical, magnetic, thermal, and mechanical (force-distance based) modes [9, 10]. Depending on whether you are teaching future electrical, mechanical, or bioengineers, one can adjust according to the needs of the major.

Teaching the “Introduction to Nanotechnology” lab, an undergraduate course, to a broad spectrum of engineering students was designed with one more idea in mind, utilizing all equipment SCU has at the Center for Nanostructures (CNS). Sections 4 and 5 give a general introduction to optical profilometry and ellipsometry. Section 6 is dedicated to transmission electron microscopy (TEM). TEM concludes the list of measurement techniques in this chapter. Section 7 provides examples of syllabus and students’ reports on the topic of “Electron Microscopy”. A graduate-level guided research course for students with a concentration in materials science was developed with a focus mainly on SEM and AFM, see Section 8.

2. Imaging with electron microscope

2.1 Basic topography

Secondary electron (SE) or reflected electron beam, is a default operating mode for commercial SEMs. The physical origin of the term belongs to the fact that when the primary electron beam hits the surface of the material, primary electrons interact with the outer shell electrons and reflect back as secondary electrons [7, 8]. The nature of image formation is frequently described in analogy to sunlight shining on the mountains producing good image contrast depending on the tilt angle of the specimen and or topography variation (see Figure 1).

Figure 1.

2.5 mm × 2 mm SEM scan of fractured CuZn alloy specimen after tensile testing.

Cross-sectional SEM imaging can reveal a wealth of information about the quality of fabrication and the root cause of failure [12]. Sample preparation for cross-sectional examination is the key to successful imaging; therefore it is essential to introduce students to this topic. For teaching purposes in undergraduate labs, the process of cross-sectional sample preparation can be simplified. It can be as simple as braking, or cutting, a wafer with a diamond knife and mounting a piece in a vertical position rather than laying it flat, see Figure 2. Students can learn how to demonstrate different types of information that can be extracted from semiconductor samples depending on how it is prepared, see Section 7 for a project example.

Figure 2.

Top view (a) and cross-sectional SE SEM images (b). (a) 2–5 nm cobalt nanoparticle (TedPella sample) and (b) cross-section of a silicon wafer showing 200 nm layer of TOX. Our measurements indicate 191.56 ± 2.12 nm.

Nanoparticle analysis is a valid option for a characterization project as well. An electron beam can be focused down to 1–2 nm, providing ultimate lateral resolution imaging of nano-scale objects with SEM (see Figure 3(a)). Unlike AFM [13, 14], SEM does not have tip artifacts associated with the size of the scanning tip, which can be an idea for a project to compare SEM resolution vs. AFM lateral resolution, see Figure 3. The topic of resolution can be expanded toward transmission electron microscopy (TEM), where the theoretical resolution of the electron beam can be achieved [1, 7].

Figure 3.

(a) 5 μm × 2 μm topography, SE SEM, scan of gold particles (TedPella Inc. sample) and (b) 1.4 μm × 1.4 μm AFM topography scan of 100 nm diameter polystyrene spheres on mica.

The standard operating voltage for SEM is between 10 keV and 30 keV, with 20 keV as a typical accelerating voltage, allowing students to stay focused on learning basic modes of operations without going too deep into imaging modes of electron microscopy [8], see Figures 1–3(a).

2.2 Atomic number contrast

Atomic number contrast or backscattered electron imaging (BSE), arises from the interaction of the primary electron beam with the atomic nucleus rather than with electron shells [7, 8]. This provides an opportunity to observe contrast based on the difference in atomic number. The higher the difference in atomic number, A, the greater the contrast. Gold nanoparticles (A = 79) deposited on graphite (A = 6) are a good reference sample for successful demonstration of BSE imaging (see Figure 4). An eutectic alloy where the difference in atomic numbers between lamellas is large enough to provide visible contrast, is another good candidate for demonstration atomic contrast, see Section 8. A CuZn substitutional alloy, in comparison, provides essentially no BSE contrast because atomic numbers for Zn and Cu are 30 and 29, respectively.

Figure 4.

(a) BSE SEM image of gold nanoparticles deposited on carbon substrate (TedPella sample) and (b) SnBi eutectic alloy showing lamellar microstructure. Brighter regions are Bi-rich (A = 83) because heavier elements dominate the composition of lamella. Darker regions are Sn-rich (A = 50) because lighter elements dominate the composition of lamella.

Most of the commercial SEMs are equipped with a BSE detector which is easy to operate. BSE contrast could provide compositional insights that are otherwise not visible with SE SEM. BSE imaging can be paired with EDS as a nice project for students to learn the pros and cons of both techniques.

2.3 Elemental mapping

Elemental mapping with EDS is a powerful tool for composition analysis. Image formation is based on X-rays emitted due to the interaction of the incident e-beam with the surface electrons [1, 7, 8]. This method allows visualization of inhomogeneities and X-ray spectrum analysis (see Figure 5). The information obtained from EDS usually compliments BSE contrast, which in its own right can be an additional project for students to do—i.e., homogeneity verification, impurities segregation and lamella microstructure study (see Sections 7 and 8).

Figure 5.

(a) EDX map of CuZn alloy, showing homogeneity of elemental distribution in solid solution and some presence of surface contaminations (C and O). (b) EDS map of SnBi alloy showing inhomogeneous distribution of Bi in Sn solid solution. (c) SnBi alloy X-ray spectrum and calculated composition of the alloy (small onset on c).

The smaller elements of microstructure become the more one needs to be aware of the size of the volume interaction in comparison to the size of inhomogeneities or nanoparticles to avoid false interpretation of elemental composition. The size of the volume of interaction is generally thought of as 1 μm³, meaning the radius of the particle should be less than 0.62 μm to provide meaningful measurements with EDX. The reported critical size is actually around 5 μm according to NIST studies referenced by Goldstein et al. [8]. If the size of the nanoparticle is smaller than the critical value, there is a good chance, the EDX image analysis software may miscalculate the composition (see Figure 6). According to the sample specification, the deposited islands are 100% gold. The substrate is 100% carbon (graphite). However, the software calculations for selected particles are 5% Au, 27% C, and oxygen is the rest (see onset Figure 6b). Nanoparticle particle size distribution, in conjunction with composition verification, is a good project for undergraduate students. You choose to use SE SEM vs. EDX or SEM vs. AFM (see Chapters 8 and 9).

Figure 6.

(a) EDX map of gold particles on graphite showing false result from selected area analysis due to size of the particle not being taken into account (b) Spectrum 1, selected area composition, particle (in red) is 1.8% Au, 26.8% C, 71.5% O. Spectrum 2, selected area composition, substrate (in yellow) is 0.5% Au, 27.1% C, 72.4% O. A nominal composition is 100% gold for particles and pure graphite as substrate.

3. Imaging with AFM

AFM is a subset of SPM that does not require a vacuum nor the probe and or sample to be conductive [5, 6, 9, 10, 11, 15]. The physics, fundamentals of operation, and modes are extensively covered in the literature [7, 8, 9]. Imaging with AFM implies a smaller scan size compared to SEM, usually less than 150 μm scans compared to a few mm, respectively (see Figure 1 for SEM and Figure 7 for AFM). The height variation is also limited to less than 8 μm due to the maximum piezo extension of the AFM scanner head. Overall sample size should be small enough to fit under the AFM scanner head, ∼2 × 0.25 inches maximum.

Figure 7.

14.5 μm × 14.5 μm 3D AFM images of the Vickers hardness indent on CuZn surface.

Novice users of AFM should be aware of AFM tip artifacts [13, 14]. The phenomenon manifests itself when the size of the features of the interest becomes comparable to the diameter of the AFM probe. The typical value for the tip radius for the most commercially available probes is ∼20 nm (compared to the size of the electron beam of 1–2 nm). This means the measured XY distances will be dilated by approximately the size of the probe. It is possible to correct for tip dilation and reconstruct the shape of the tip of the probe by running your data through the tip dilation algorithm [14] (see Figure 8).

Figure 8.

(a) 1.6 μm × 1.6 μm original AFM scan of 102 nm diameter spheres (b) reconstructed image of the spheres without tip dilation effect. Reproduced with permission of springer nature. Images are courtesy to Wong et al. [14].

3.1 Basic topography

There are three main AFM topography modes:

1. contact mode or non-vibrating mode

2. non-contact vibrating mode

3. in-and-out of contact vibrating mode, commonly referred as Tapping mode (the term coined and trademarked by Veeco in about 2000–2010).

The AFM probe, or stylus, moves over the surface of the sample tracking the topography similar to a mechanical profiler that metallurgists used to measure surface roughness on the macro and micro scale. The benefits of the light lever amplification being used to decern up-down motion on a position-sensitive photodetector to acquire topography data. The probe is kept in feedback with the electronics maintaining either force of interaction between the sample and the probe constant or distance from the tip to the sample constant [9, 10, 15, 16]. It usually takes an experienced user to prefer one type of feedback loop versus another. The software makes it easy to switch from one feedback setting to another.

The choice of the most appropriate mode of operation, as well as the AFM probe, depends mainly on your sample. If the sample is hard and dry (metals, alloys, ceramics, and hard plastics), then contact mode and contact probe will do a good job. If your sample is a delicate soft polymer or integrated circuit or some biological tissues, then oscillating modes and probes will be your choice. It is easier for students to start with contact mode first and then switch to vibrating mode while practicing on the same reference samples, see Figures 9–11. Once students master routine imaging, they can switch to actual samples and do projects (see Figures 3b, 8, 12 and 13).

Figure 9.

(a) 100 μm × 100 μm AFM scan of Veeco reference sample. Pitch size is 10 μm, depth is 100 nm. (b) 13 μm × 13 μm AFM image of a reference sample (TedPella, 3 μm pitch size, nominal step height = 100 nm). Step height measurements, 94 nm, are shown with histogram method.

Figure 10.

A typical selection of channels recommended for contact mode scanning. From left to right: topography, LFM or friction, deflection, or error channel and scan parameters tab. Both LFM and error data should be monitored in both scan directions for good image quality.

Figure 11.

A typical selection of channels recommended for vibrating mode scanning. From left to right: topography, phase, deflection, or error channel, and scan parameters tab. Both Phase and error data should be monitored in both scan directions for good image quality.

Figure 12.

50 μm × 50 μm sanning capacitance mode (SCM) images of the cross-sectioned MOSFET (a) relative dopant levels contrast, bright-low dopant level (b) dopant type contrast, brown—n-type, white—p-type, (c) combined SCM image. Images are courtesy to Eurofins EAG Laboratories.

Figure 13.

(a) 10 μm × 10 μm topography image of an indent done with Berkovitch tip by a Nanoindenter. Scanning is performed with a Nanoindenter right after indentation and (b) error channel image acquired simultaneously with topography channel.

3.2 Lateral force mode (LFM)

There are two built-in additions to topography imaging: lateral force, or friction, mode (LFM) and phase mode, which can be acquired simultaneously with topography. LFM and phase images are related to the physical properties of the materials under investigation.

The signal that feeds the LFM channel is associated with the lateral twist of the probe: Left-right motion as opposed to the up-down motion associated with the topography channel. The amount of twist or the difference in intensities between left and right quadrants in position-sensitive photodetector can be correlated to drag force or the friction coefficient of the material [9, 10]. LFM contrast can represent the difference in friction coefficients of the materials or the amount of twist due to large height variation (see Figure 10). The error (deflection) channel should not be forgotten during the acquisition as it represents the quality of feedback loop parameters adjustment. It is good practice for students to acquire data having topography, LFM, and error channels open.

3.3 Phase contrast in vibrating modes

In vibrating mode, the simultaneous data acquisition channel is called the phase channel. The feedback loop in oscillating mode can work either on amplitude or on phase signal, therefore the phase channel (usually the default setting) records the phase delay of the signal made with the material of interest [9, 10]. The topography channel represents recording of height variation on constant amplitude with respect to the driving signal. It is easy to switch the setting from phase to amplitude feedback and record amplitude attenuation while having topography imaging done in constant phase. Triblock polymer sample is usually the best candidate for phase image verification. However, even a mildly contaminated reference sample can do a good job (see Figure 11). Phase image represents the phase signal delay associated with differences in hardness, elastic modules and adhesion of the material and results in corresponding image contrast.

3.4 Material sensing modes

The material sensing modes are thenext generation of AFM capabilities. AFM can visualize the mechanical, magnetic, electrical (see Figure 12), and thermal properties of materials [9, 10]. An in-depth discussion of material sensing mode is beyond the scope of this chapter; however, we would like to illustrate a couple of important applications: electrical mode and indentation.

AFM can measure long-range interaction forces, such as electrostatic force and force gradient. One of the variations of electrical AFM (EFM) is scanning capacitance microscopy (SCM). SCM maps charge distribution with a lateral resolution sufficient for the needs of the semiconductor industry (see Figure 12).

Indentation studies are a promising domain of AFM-based techniques. The best way to measure nanohardness and elastic modulus is to use a Nanoindenter. Nanoindenter is an instrument, especifically designed to perform hardness measurements on the nanoscale. If a Nanoindenter is at your disposal, then it is very useful for teaching students about the difference between AFM and Nanoindenter. Figure 13 shows images of an indent performed with a Nanoindenter. Nanoindents have a distinct triangular pyramid shape reflecting the geometry of a diamond indenter, Berkovich tip. Vickers hardness indents have the characteristic shape of a square pyramid while Berkovich indenter is 3-sided pyramid (compare Figure 7 and Figure 13). Hardness mapping of bonding areas of micro and nano interconnects is of interest in the semiconductor industry [17, 18].

4. Imaging with optical profilometer (complimentary method)

A profilometer is a device similar to a phonograph that measures a surface as the surface is moved relative to the contact profilometer’s stylus. A profilometer is an instrument used to measure a surface profile, to quantify its topography. Critical dimensions as step height, curvature, flatness, and surface roughness are computed from the surface topography. Profilometry branches out to SPM where the stylus is a scanning probe or cantilever of very small size. SEM utilizes an electron beam as a scanning probe [5, 6, 7, 8]. Optical profiler is based on light and light interferometry [19, 20].

Optical interferometry is a physical phenomenon when the wavefront of light reflected from the surface of the material interferes with a reference wavefront. By introducing a slight tilt to one wavefront, a pattern of interference fringes is created. The departure from the straightness of these fringes is a deviation from a reference. Sophisticated software can reconstruct the 3D topography of the surface based on the difference in interferometry patterns.

4.1 Step height and surface roughness measurements

Metrology parameters, such as step height and surface roughness, can be quantified with the optical profiler (see Figure 14). The scan range overlaps nicely with SEM and AFM. Pairing the optical profiler technique, either with SEM or AFM, represents a valuable teaching opportunity where students can explore the limits of resolution for different techniques and merge substantial characterization data sets together (see Sections 8 and 9).

Figure 14.

Screenshot of optical profilometry images (2D, top right, and 3D, down right) with line profile and surface roughness measurements (top left). The height measurements result in 615 ± 2 μm tall silicon trench. The average surface roughness S_a = 5.3 μm. RMS surface roughness S_q = 6.9 μm.

4.2 Advantages and disadvantage of optical interferometry

An optical profiler is a non-contact and fast method to visualize surface topography from micro- to upper nano-range. The techniques were most suitable for delicate and, or, organic samples that cannot be touched by a mechanical stylus. 3D image is reconstructed from interference patterns. The imaging may be problematic for transparent, highly reflective materials and true nanoscale features.

5. Ellipsometry (complimentary method)

Ellipsometry is a standard industry technique to measure the thickness and other properties of thin layers of dielectrics and semiconductor materials [21]. The fundamental principle of ellipsometry is the phase difference between two mutually perpendicular polarized light beams. The information about the sample is contained in total reflection coefficients. The quantities such as thickness and optical constants are calculated based on assumed theoretical models.

5.1 Optical properties evaluation and film thickness measurements

Both thickness of a film, or layer, in layered structure and refractive index can be evaluated with ellipsometer, if the films are optically transparent (see Figure 15).

Figure 15.

Ellipsometry user interface for TOX wafer reporting thickness 549 nm ± 26 nm and refraction index n = 1.4 ± 0.2.

5.2 Advantages and disadvantages of ellipsometry

An ellipsometer is simple to use. The measurements are highly reproducible and very sensitive to the presence of ultrathin films (down to a monolayer or native thermal oxide on silicon). An ellipsometer can be used to analyze multiple layers and determine the optical constants of unknown materials. Ellipsometry is not an imaging technique.

6. Transmission electron microscopy

TEM is considered to be a more difficult technique than SEM requiring preparation of a very small and delicate sample. Visualization and image interpretation requires an understanding of geometrical optics and diffraction fundamentals [1, 7]. There are three basic mechanisms of TEM contrast formation: mass-thickness contrast, diffraction contrast, and phase contrast [7]. All three contributing factors may form an image. The resolution of TEM is near the theoretical limit (0.2A) for an electron beam at 100 kV [7]. TEM compliments high-resolution SEM (1–2 nm) and is much better than AFM, which has limited lateral resolution (∼20 nm) due to tip artifacts [14]. Mass-thickness contrast is most frequently used as images are relatively easy to interpret (see Figure 16). Diffraction and phase contrast has been extensively used by physical metallurgists to study dislocations, staking faults and other crystallographic phenomena [7, 23]. A combined TEM/SEM/AFM project can be a suitable candidate for graduate lab or guided research [24]. We plan to outline briefly only the importance of diffraction patterns for practical applications and discuss a special case of using superlattice reflections from a diffraction pattern to form dark field image [7].

Figure 16.

Bright field TEM images showing lead dioxide particles with hexagonal shape, deposited on silicon. Reproduced with permission of the International Union of Crystallography. Image is courtesy to Kabbara et al. [22].

6.1 Bright field imaging: mass-thickness contrast

Mass-thickness contrast results from electrons that pass through the specimen. The electrons having no obstacle, or a very thin layer of material, on their way after passing the objective aperture result in a bright (white) color appearance of the recording film. A thicker specimen will allow the transmission only a portion of electrons and will result in a darker color of the film due to less exposure to electrons. The layer, or specimen that are too thick will block electron beam and film will appear dark, because all electrons are blocked by the specimen (see Figure 16). Biologists usually prefer mass-thickness contrast by taking advantage of staining cells with heavy elements. CNTs, graphene, precipitates and nanoparticles can be successfully studied with TEM [25, 26, 27, 28, 29].

6.2 Use of diffraction patterns

Diffraction patterns by themselves can be very useful to indicate if partial crystallinity is present in the compound. A single crystal will form dots on a diffraction pattern (see Figure 17), polycrystalline material will produce rings and amorphous materials will result in a fuzzy halo [7]. Indexing the diffraction patterns is a routine job of a crystallographer requiring knowledge of both crystallography and the physics of electron diffraction [1, 7]. The project involving indexing or use of the diffraction patterns would be a good candidate for a graduate research assignment.

Figure 17.

(a) Indexed TEM diffraction pattern in [100] orientation and (b) indexed TEM diffraction pattern showing superlattice reflections, see arrows pointing at weaker reflections. Reproduced with permission of the International Union of Crystallography. Images are courtesy to Woodward and Reaney [23].

6.3 Dark field imaging

Dark field imaging in general means that in the absence of the specimen, the background appears dark because all electrons are blocked by the shifting objective aperture of the TEM microscope [7]. This is a special case of kinematic diffraction contrast when only electron “light” resulting from super reflections is used for image formation (see Figure 18). Dark filed imaging is an essential technique to study morphology and kinetics of coarsening of ordered precipitates in a disordered alloy matrix [25, 26, 27].

Figure 18.

500 nm × 500 nm dark field TEM images of Ni₃Ga precipitates in NiGa single-crystal alloy as a function of aging time. Left image is the shortest aging time, right image is the longest aging time for the same alloy composition. See data analysis in [27]. TEM images are courtesy to Dr. Starostina.

7. “Introduction to Nanotechnology” course example

Course description: “Introduction to the field of nanoscience and nanotechnology. Properties of nanomaterials and devices. Nanoelectronics: from silicon and beyond. Measurements of nanosystems. Applications and implications. Laboratory experience is an integral part of the course.”

7.1 Lab syllabus example for undergraduate course

“MECH/ECEN 156 “Introduction to nanotechnology” lab.

Course type: elective, undergraduate level engineers, contribute to engineering topics.

Learning outcomes:

• hands-on experience operating scientific instrumentation

• hands-on experience acquiring data on nanoscale

• being able to choose a proper material characterization technique(s) to meet the requirements of the project

• technical presentation design: ability to create technical presentation

• presentation skills: ability to communicate technical results of your project

Instrumentation: The course is based on the instrumentation available at CNS and other laboratories. It includes optical profiler, AFM, electron microscope, probe station, and other equipment.

Group size: 2–3 people per group, no more than 5 groups (15 people max).

Projects (examples):

1. Electrical and ellipsometry characterization of the thermal oxides and MOS-structures.

2. Ellipsometry and SEM/EDX of the thermal oxides in cross-section.

3. Nanoparticles morphology and particle size distribution characterization.

4. Metrology and surface roughness characterization from micro to nano.

5. Electrical and SEM characterization of MOS-structures.

Preliminary schedule

Week 1 Introduction and safety training at CNS.

Week 2–week 6 Group training on instruments, hands-on practice on test samples (rotating stations every week; one week per instrument, if done earlier can start doing a project).

Week 7–9 projects measurements—done on at least two different instruments/different types of complementary measurements.

Week 10 field trip if arrangements with nanotechnology company are possible.

7.2 Lab reports, SEM example

The video recordings of “Introduction to Nanotechnology” final exam, mini-conference, can be seen online [30, 31, 32, 33, 34]. The video recording of Ph.D. student poster presentation, “Influence of Crystallographic Orientation on the Growth of Thermal Oxide of Silicon”, inspired by teaching this lab is available on the official AAAFM YouTube channel [35].

“Scanning electron microscope laboratory report”

Instrumentation description

Hitachi S4800 Scanning Electron Microscope. The SEM works, primarily, by sending a beam of high-energy electrons from an electron gun, through electromagnetic lenses and apertures which manipulate the electron beam (alignment, stigma, and focus) onto the target sample. The electrons interact with the sample in various ways to produce secondary electrons, backscattered electrons, and X-rays. The signals from these interactions are collected by one or more sensors and processed into an image for viewing. In the case of the X-rays, information about the elemental makeup of the sample can be determined and superimposed on a secondary electron image. This is a non-destructive process that can produce great information about the surface of a sample in a relatively short amount of time. (Description of my own based on information from Wikipedia and Nanoscience Instruments.)

Results

The initial image at 15K magnification, see Figure 19a, was clear and as expected with great care taken during the alignment phase. However, an issue arose a short while later that caused the image from the SEM to shift erratically. This nuisance shifting made further alignment very difficult. The 100K magnification image, see Figure 19b, likely suffered some resolution quality due to this and the image capture used for the EDX was mostly unrecognizable. But the EDX was able to provide some good information on the sample surface, see Figure 19c. Carbon was present due to the carbon nanotubes, silicon and nickel were present as they are the substrate elements upon which the nanotubes are grown, and oxygen was present perhaps due to some oxide layer on the substrate or oxygen contamination from sample exposure to the atmosphere. The nanotubes appear to range from 50 to 200 nm and have an approximate density of 1.24E10/cm².

Figure 19.

(a) Low magnification, 15K, SE SEM image of MWCNTs grown by PVD method. (b) High magnification, 100K, SE SEM image of MWCNTs grown by PVD method. (c) Screenshot of EDS window analysis showing elements detected.

8. “Experiments in materials science” guided research lab example

Course description: “This course consists of research-oriented assignments involving heavy use of scientific instrumentation mainly at the center of nanostructures (CNS) and is equivalent to culminating experience. The projects are sample/materials-based. The assignments may involve hands-on sample preparation, instrumentation calibration verification on the reference samples, imaging and measurements followed by data analysis. The research may include hands-on examination of surface morphology/roughness and elemental composition and mechanical properties. Students are expected to correlate obtained data of structural and compositional changes on micro/nano scale to changes in materials properties. The results of the assignments are expected to be written up in a scientific paper format and presented thereafter. An off-campus tour may be organized if arrangements are possible.”

8.1 Syllabus example for graduate course

“333B “Experimental Analysis in Materials Science”

Course type: elective, graduate-level engineers, contribute to engineering topics.

Course learning outcomes:

Students who successfully complete MECH 333AB will be able to:

• choose a proper material characterization technique(s) (optical-light microscopy, AFM, electron microscopy) to meet the requirements of your research project

• hands-on experience operating scientific instrumentation

• technical writing: ability to write in a technical paper format

• technical presentation: ability to create technical content for a public presentation

• presentation skills: ability to communicate technical results of your project

Group size: 2–3 people per group, no more than 5 groups (15 people max).

Examples of research assignments:

• SnBi alloy micro/nanostructure morphology, chemical composition, and mechanical properties evaluation

• Grain size, morphology, chemical composition examination, and dihedral angle of twin boundary measurements in CuZn alloy

• Gold nanoparticles size distribution, morphology and chemical composition characterization

8.2 Example of students reports abstracts and results

The video recordings of “Experiments in materials science” final exam, mini-conference, can be seen on-line [36, 37, 38]. Dihedral angle measurement with AFM project and morphology measurements of eutectic in SnBi alloy resulted in publications in peer-reviewed journals [24, 39].

“Characterization of Gold and Cobalt Nanoparticles using AFM and SEM”

Authored by Brian Chen, Raymond Chen, Mohamed Sabry

Abstract

Understanding nanoparticle morphology and chemical composition is critical to predict the behavior of these particles in various applications. In this chapter, SEM, EDX, and AFM were used for characterization. Gold and cobalt particles were purchased from Ted Pella and are known to be deposited using thermal evaporation method. Cobalt spec is 5–7 nm for height distribution. As for gold, there were two samples used, 2–30 nm and 30–500 nm. SEM was used to determine the morphology parameters of gold particles such as size, aspect ratio, and sphericity. Average size was 14 and 18 μm for smaller and larger particles respectively. The aspect ratio was 1.37–1.48 for smaller to larger particles. Sphericity is 0.827 and 0.69 for smaller and larger particles. The values are an average value based at least 50 measured particles. EDX was used for elemental composition analysis of different areas as well. AFM was implemented for cobalt topography measurements using two different scan areas 1 × 1 μm and 375 × 375 μm. A total of 30 particles are measured to calculate the average height and PSD. The average height measured is 13.9 nm. Particle size distribution (PSD) is between 10.8 and 16.89 nm. The measured data for cobalt were found to be outside of the vendors specifications, while gold seems to deviate from the normal distribution. In this chapter, some of the suspected reasoning for this discrepancy will also be discussed. After all the data was analyzed, recommendations for best techniques to characterize the properties of nanoparticles is given.

9. Conclusions

The product management approach proved to be a very useful tool for designing and developing a laboratory practicum. Our ultimate goal was to utilize SEM in all modes available at CNS to verify the measurements done with AFM. Our second priority was to use all scientific instrumentation at CNS to compliment both SEM and AFM, enhancing the dual, or complementary, measurement idea. Our third priority was to make the undergraduate lab as well-rounded as possible in order to be able to include students from Physics, Mechanical, Electrical, and BioEngineering departments. The priority for the graduate course was to be able to generate a sufficient amount of data for further analysis and ultimately publication in a peer-reviewed journal. We also are very mindful of students having hands-on experience with microscopes by implementing “stations rotation” mechanism to move a cluster of students from one microscope (characterization technique) to another characterization technique. By doing that we were able to train students on five instruments, enabling them to conduct research projects with minimum assistance.

The outcomes of our product-oriented approach resulted in two successful courses based primarily on SEM and AFM with publications in peer-reviewed journals with students as co-authors. The dual design idea can be expanded to AFM materials sensing modes with complements of Scanning TEM and or to the fields of chemistry and biology. Both SEM and AFM can be integrated into projects involving nanomanipulation.

Acknowledgments

We acknowledge the contributions of Prof. Drazen Fabris and Prof. Shoba Krishna for setting ultimate goals and funding the MECH/ECEN156 and MECH 333B courses, Dr. Stephen Hudgens for fruitful discussions, Dr. Michael McElfresh for proofreading the manuscript, Dr. Robert Marks for supplying SnBi and CuZn samples. We acknowledge the contributions of Eurofins EAG Laboratories for sharing SCM images. Copyright Eurofins Scientific. www.eag.com

A special thanks for the commitment and dedication of our Student Assistants for these course—Parth Shah for SEM/EDS, Dongmeng Li for Optical Profiler and SEM/BSE/EDS and Vinay Krishnan for AFM. We also would like to thank SCU School of Engineering Dean’s Office and Office of Diversity & Inclusion for funding this publication.