A Fine Measurement Machine Integrating Nanotechnology into the K-12 STEM Curriculum Rob Snyder

Atomic Force Microscopes (AFMs) are used to make nanoscale measurements. AFMs and other technologies will be seen during tomorrow’s tour of the Center for Hierarchical Manufacturing here at UMass Amherst.

An AFM generated this image of the surface of glass. This is a 20 μ x 20 μ image 20 micrometers = 20 x 10-6 meters = 20,000 nanometers The surface was mapped to a depth of 420 nm 420 nanometer = 420 x 10-9 meters http://en.wikipedia.org/wiki/Atomic_force_microscopy

An Atomic Force Microscope has three essential features. A cantilever arm that includes a tip that causes the arm to flex when the tip is brought very close to a surface. A mirror that creates a long pathway for a reflected beam of light. A device that detects changes in the direction of the beam of light.

An AFM has even been transported to Mars. This image presents data from the AFM on NASA's Phoenix Mars Lander. It shows surface details of a substrate on the microscope station's sample wheel. It will be used as an aid for interpreting later images of minuscule Martian soil particles. Source: http://www.nasa.gov/mission_pages/phoenix/images/press/First_AFM_on_MARS.html

K-12 STEM programs typically do not have the resources or facilities to conduct actual nanoscale science and engineering investigations using AFMs. The base price for this desktop AFM sold by AFM Workshop is $26,450. (afmworkshop.com). Additional expenses would include creating a designated work area, maintenance, etc.

However, there are opportunities for students to conduct investigations with a model of AFM that: Meet criteria of the National Research Council’s Framework for K-12 Science Education. The “Framework” guided the development of the Next Generation Science Standards. Meet criteria of the Performance Expectations of the Next Generation Science Standards. The “NGSS” serves as guide for revisions of many state and local STEM learning standards. Develop an understanding of fundamental scientific principles and processes that are the focus of typical middle school and high school STEM lessons and investigations.

We experimented with using Legos to construct a model of an AFM. The structure required the assembly of lot of Legos and had a tendency to collapse at any moment.

A simple lever can be used as a model of an AFM even though it has a rigid lever arm rather than a flexible cantilever arm.

These are the components of the lever system.

You will need to: Assemble the lever mechanism so that it can be used to measure the thickness of an object. Calibrate the lever mechanism using objects with a known thickness. Develop a strategy to determine the thickness of other objects. Suggest or develop strategies for improving the effectiveness of the fine measurement machine.

\ The support for the lever and a hanging mass need to be placed in positions so that the end of the long lever arm does not exert a lot of downward force on an object being measured.

Laser Pointer Lever support mirror Hanging mass A sheet of paper A sheet of paper on a wall can be used to mark the positions of points of light when objects of known or unknown thicknesses moves the lever mechanism.

Several data points should be recorded for each calibrating and experimental trial. Note: The reflected laser light will not be a point of light on the sheet of paper. It will have the appearance of a diffraction pattern.

When a thin object moves under one end of the lever arm it causes the lever arm to move a short distance. The laser light reflected onto a sheet of paper on a wall moves a greater distance. The reflected light beam now reaches a different point on the ruler.

Shims with a known thinness can be used to calibrate the measurement machine. The calibration reveals the relationship between the movement of the lever and the movement of the point of light on the ruler. How might students use sheets of photocopier paper be used to calibrate the lever mechanism?

Share ideas about how to conduct the investigation.

A few suggestions Lever mechanisms need to be positioned so that each group’s reflected beam of light can reach a wall. Use painter tape to place a sheet of paper on a wall so that the tape can easily be removed. Work with the laser pointers carefully. Keep the lever mechanism in one location and stable while collecting and recording data. Avoid interrupting a reflected beam of light of other groups.

Share ideas for analyzing data when trying to determine the thickness of unknown objects.

You can explore how extending the path of light affects the measurement process. Another Mirror Ruler ruler

An example of an engineering/design question in the activity: How could a support be designed for a cantilever system?

Examples of Disciplinary Core Ideas from the Framework The path that light travels can be traced as straight lines, except at surfaces between different transparent materials (e.g., air and water, air and glass) where the light path bends. (MS-PS4-2) All positions of objects and the directions of forces and motions must be described in an arbitrarily chosen reference frame and arbitrarily chosen units of size. In order to share information with other people, these choices must also be shared.(MS-PS2-2) An example of a Crosscutting Concept from the Framework Much of science deals with constructing explanations of how things change and how they remain stable. (HS-PS1-6)  

An Example of a NGSS Performance Expectation   MS-PS2-2. Plan an investigation to provide evidence that the change in an object’s motion depends on the sum of the forces on the object and the mass of the object. [Clarification Statement: Emphasis is on balanced (Newton’s First Law) and unbalanced forces in a system, qualitative comparisons of forces, mass and changes in motion (Newton’s Second Law), frame of reference, and specification of units.] [Assessment Boundary: Assessment is limited to forces and changes in motion in one-dimension in an inertial reference frame and to change in one variable at a time. Assessment does not include the use of trigonometry.]

Students can develop a strategy for measuring and comparing the angles of incidence and reflection. Angle of Incidence Angle of Reflection Normal Line ruler

Mathematical relationships can be discovered. Long light path and a short cantilever gives large amplification laser d2 pivot point L2 . cantilever L1 d1 The distance amplification d2/ d1 is proportional to L2/ L1

This activity could be a part of a study of the gravitational forces acting on a lever system. Point of Rotation Students in a physics course could use their understanding of balanced torques to calculate the weight of the mirror.

It important to note that forces other than gravitational force become very important when the tip of a real AFM is mapping a surface.