introduction for a lab report

Experiment 1

Crystallography and Crystal Structure

Purpose

To understand the concepts of crystal structure, atomic packing, and Miller Indices as well as

their applications in materials properties and development. Differences and similarities between

crystal structures of metals, ceramics, and polymers will be studied.

Apparatus

None

Specimens

Crystalline Structure Building kit.

Background

This experiment will include both individual work and collaborative work with the laboratory

team partners. The objective of this experiment also includes knowing the lab partners as the

team will be working together for the remainder of the semester. Crystallography kits are

available in the laboratory. These kits consist of various Styrofoam balls that will be used to

construct the crystalline structures.

The objective of this experiment is studying the following atomic structures:

 Simple Cubic

 Body Centered Cubic

 Face Centered Cubic

 Hexagonal Close-Packed

For each atomic structure, you should:

 Identify and draw the repeating pattern of planes identify and draw the unit cell in your

lab notebook.

 Identify the number of atoms per unit cell and record this in your notebook.

 Identify and draw distinguishing characteristics of the unit cell in your notebook.

 Identify the crystal structures of ceramics and polymers.

 Identify the differences between the crystal structures of metals, ceramics and polymers.

 Identify the close-packed planes in each of the crystal structures studied in the

experiment.

Each person in the lab group should take a handful of the Styrofoam "atoms." Each Laboratory

Group needs 10-15 balls. Arrange those atoms in as many different ways as you can in a single

plane. See how many combinations of these planes you can come up with. Identify which crystal

structure each of these results in. Which ones have a lot of empty space? Which ones have very

little empty space?

Activity Objectives and Outcomes

 The objective of this experiment is to model the different crystal planes for better visualization of

the Miller indices. By the end of this activity you should be able to understand and visualize the

basic crystal planes in a crystal structure and match the correct Miller indices to each plane.

Supplies / Equipment

Supplies for each team (provided by instructor)

3 sticks or rulers (representing the x, y, z axes)

1- piece of cardboard approximately 12"x12" in size (representing a “plane”)

1 – 18” piece of string (representing a “vector” or direction)

This activity should be performed in teams of 2 or 3 in order to promote discussion and a better

understanding of the concept.

Documentation

Answers to the Post-Activity Questions

An on-line tutorial

Below is an on-line tutorial that will help you to better understand Miller Indices before starting

the activity.

Lattice Planes and Miller Indices

(http://www.doitpoms.ac.uk/tlplib/miller_indices/printall.php), University of Cambridge. Southwest Center for Microsystems Education (SCME) Page 7 of 10

Fab_Crystl_AC00_PG_112913 The Miller Index Activity

Activity: Miller Indices Models

Procedure

1. Have one or two members of your team create a Cartesian

coordinate system using the three rulers. Each ruler represents the

x, y, or z axis. For the purpose of this exercise, use the Cartesian

orientation shown in the "Crystal Planes" image shown previously

in this activity. Make sure that your team members know which

ruler represents which axis (x, y, or z).

2. While one member of your team holds the axes, another should

position the piece of cardboard perpendicular to and in the middle of

the "x" axis (1 unit length), and parallel to the y-z plane. The

cardboard in this orientation represents the (100) crystal plane.

3. Position the piece of cardboard perpendicular to and in the middle of your "y" axis. The

distance should represent 1 unit length. The cardboard in this orientation represents the

(010) crystal plane.

4. Position the cardboard to represent the (001) crystal plane. Make sure that everyone in

your team agrees.

5. Position the cardboard to denote the (110) crystal plane. Make sure that everyone in your

team agrees.

6. Now position the cardboard in the (111) orientation.

7. Model the (1̅00), (01̅0) and (001̅ ) planes. 8. Model the (101), (011), (101̅), (11̅ 0) and (011̅ ) planes. 9. Using the string, model the following vectors or directions.

[100], [010], [001], [011], [110], [111]

Southwest Center for Microsystems Education (SCME) Page 9 of 10

Fab_Crystl_AC00_PG_112913 The Miller Index Activity

Post-Activity Questions

1. What does it mean when a crystal plane is noted like this: (1̅00)?

2. Name all of the faces of the "unit cell" using the Miller Index notations.

3. Draw a unit cell and show the (011) plane relative the x-y-z axes.

4. Draw the (101) plane relative the x-y-z axes.

5. Using Miller indices, name the following crystal plane, relative to the unit cell.

6. Using Miller indices, name the following crystal plane, relative to the unit cell.

1. Using Miller indices, name the following crystal plane, relative to the unit cell.

Southwest Center for Microsystems Education (SCME) Page 10 of 10

Fab_Crystl_AC00_PG_112913 The Miller Index Activity

Summary

Crystal orientation is a very important aspect of microsystems fabrication. Knowing the

orientation of a crystal is imperative to being able to design and fabricate functional

microstructures because the physical, chemical and electrical properties of each plane can be

different. The Miller Index allows us to identify and notate specific crystalline planes relative to

the Cartesian coordinate system and the unit cell.

References

1. Gallium arsenide. Wikipedia. 2011. http://en.wikipedia.org/wiki/Gallium_arsenide

2. Lattice Planes and Miller Indices. University of Cambridge.

http://www.doitpoms.ac.uk/tlplib/miller_indices/printall.php