HOMEWORK 4, NANO203
DUE March 14, 5 pm
1. (20 points) You are working on alloyed plasmonic nanoparticles, focusing on making smaller nanoparticles to increase the total surface area for increased sensitivity and activity in sensing and catalysis, respectively.
a. Identify and describe a characterization approach (technique and expected contrast/analysis mechanism) to assess the composition and structure of colloidal Cu-Au alloy nanoparticles (<30 nm) using an electron microscopy approach.
b. What signal might you use to study the dielectric response of the Cu-Au nanoparticles for application in alloy plasmonics using a TEM?
2. (30 points) Index the first 4 Bragg reflections (hkl) for the Au foil (a = 4.08 Å) diffraction shown below and calculate the camera length of the microscope at 200 kV. Perform the analyses on the printout copy of the pattern (or make absolutely sure you’re viewing at 100% size on the computer screen).
4. (50 points) The following is a diffraction pattern of a single crystal of (FCC) copper.
a. Use the measurement of distances and angles to index the three spots shown in the right half of the pattern using a camera constant of 58.5 Å-mm. Show your work. Correct your indexed peaks to ensure that the angles between them are consistent with the law of cosines.
b. What is the zone axis of this pattern?
Perform the analyses on a printout copy of the pattern (or be very sure you are viewing the pattern at 100% size on the computer screen).
5. (50 points) Applying concepts to new techniques: In the state-of-the-art low-dose atomic resolution electron microscopy reproduced below from Rothmann et al.
Science 370, eabb5940 (2020) [DOI: 10.1126/science.abb5940], the researchers used the less-common STEM technique known as Low-Angle Annular Dark Field (LAADF) to collect their images of CH(NH2 )2 PbI3. By referencing the manuscript and using your knowledge of characterization and electron-matter interactions, answer the questions below:
a. Why is LAADF advantageous for imaging of the organic cation (CH(NH2 )2+, green circle/sphere) relative to HAADF?
b. Why does Bragg diffraction contribute to the LAADF signal? Does Bragg diffraction contribute to HAADF? How do the researchers filter data to analyze structure (you’ll need to read into the article a bit)?
c. Panel D is produced by a Fourier transform. of the real space image in panel A.
i. What appears in the image in panel D and why?
ii. Based on D, what is the lattice type of the crystal?
iii. Based on D, what direction we are viewing the crystal in A?
6. (50 points) EELS, EDS, and XAS.
a. Contrast the principal characteristics of EDS and EELS spectra, especially the energies at which we find peaks.
b. What are the physical mechanisms that generate the signal and how are the results interpreted or quantified?
c. What advantages does EELS provide over EDS? Why is it particularly well suited for light element analysis?
d. Can we measure heavier elements, e.g. the 3d transition metals using EELS, and if so how?
e. How are EELS and XAS similar and how do they differ?
7. (15 points) Technique Selection Basics
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Full technique name
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Typical Spatial Resolution (order of magnitude, specify if different in the 3 dimensions)
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Mechanism Of Contrast
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Of structural, chemical, and imaging insights, this technique is most commonly used for evaluating:
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SAED
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STEM-EELS
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HRTEM
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HAADF
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