EGR 115 – Fall 2013
0. Defining Roughness
This is to be completed individually.
In the NanoRoughness_AnswerSheet.docx file, answer the following questions:
a. What procedure might you use to measure the roughness of the pavement on a road?
b. Give an example (other than road pavement) of something for which degree of roughness
matters.
o For your example, why does the degree of roughness matter?
o How might you measure the roughness (or lack of roughness) of this object?
c. How do you define roughness? Does the definition of roughness change when you think
about different objects for which roughness might matter? Why or why not?
1. Atomic Force Microscopy Background
This is to be completed individually.
Read the following explanation about Atomic Force Microscopy and IN YOUR OWN
WORDS answer the following questions in the answer sheet document.
a. What are the three modes of the AFM, and what are the advantages/disadvantages of
each?
b. What is the AFM resolution limit?
c. What causes the resolution limit?
Atomic Force Microscopy (AFM) 1
The primary purpose of Atomic Force Microscopy (AFM) is to quantitatively measure nanoscale surface features and forces with a nominal 0.1 nm lateral and 0.05 nm vertical
resolution on all types of samples. AFM works essentially like an old-school record player the kind used to play music recorded on vinyl. A high-tech version of the old-school record
player stylus moves over a surface of interest and the behavior of the arm supporting the
stylus is translated into measurements. In AFM, the stylus is called a cantilever tip.
The probe is an etched silicon or silicon nitride chip with a cantilever extending from the
chip and a sharply etched cone, known as the tip, located on the underside of the cantilever.
As the cantilever tip approaches the surface, it experiences an initial attractive force
1
References:
Phil Russell, Dale Batchelor, John T. Thornton “SEM and AFM: Complementary
Techniques for High Resolution Surface Investigations” 2004, AN46, Rev A1, Veeco
Instruments, Santa Barbara, CA.
EGR 115 – Fall 2013
(polarization forces), which is replaced by a repulsive force as the tip makes physical contact
with the specimen. A laser focused on the backside of the cantilever monitors the
displacement of the probe and provides feedback as the probe scans across the sample
surface. The probe is perpetually scanned across the sample surface either in contact with the
surface (Contact Mode), at a constant distance (Noncontact Mode), or while the cantilever is
oscillating at a defined frequency (Tapping Mode). These modes are demonstrated in Figure
1. All three modes map the topography of the surface although each has limitations and
advantages. Contact Mode can directly measure surface forces, opening the door to
calculating adhesion and friction forces at the nanoscale, but can damage sample surface.
Tapping Mode has the lowest surface forces and can provide detailed information about the
difference in surface phase behavior, thus allowing biological and soft polymer samples to be
characterized. AFM can be used to image surfaces with atomic resolution as well as surface
forces at nano-Newton scales.
The shape and radius of the cantilever tip limits the resolution of the topography images
captured from AFM. A sharper tip follows the hills and valleys of the surface more closely,
leading to better resolution than scanning with a blunter tip. Similar to feeling with your
fingertip, a sharp tip can response to a change in surface height, while a blunter tip, similar to
your elbow, overestimates large differences and neglects smaller differences (demonstrated
in Figure 2).
Depending on the AFM design, piezo scanners either translate (move) the sample under the
cantilever or the cantilever over the sample. As the cantilever tip scans the surface, the
cantilever arm responses to differences in sample height by deflecting the laser center on the
backside. The difference in deflection is measured and translated into height data, thereby
constructing a three-dimensional topographical map of the surface by plotting the local
sample height versus horizontal probe tip position. Thus, AFM images are resolved in three
dimensions and the difference in surface features can be quantified.
A
B
C
Figure 1: Three modes of the AFM: (A) contact, (B) non-contact, and (C) tapping.
The AFM outputs are shown below each diagram. The black arm represents the
cantilever beam, and the triangle represents the probe tip.
EGR 115 – Fall 2013
Figure 2: Interaction between a sharp tip and a surface feature of a sample, showing
the resolution limit of the AFM. (The top, thin, line is the output of the AFM. Note
the shallower depth of the same well for the wider tip.)
Comparison of AFM to Other Common Techniques:
Scanning Electron Microscopy images the sample using electrons reflected and refracted
from the surface layer. Samples must be coated in a conductive layer (typically gold) and
placed in a vacuum chamber (typically 10-6 torr). SEM has similar lateral resolution of
images (0.7nm) but views surfaces on a focus plane, thereby limiting the depth of focus in a
single image. Direct height measurements of surface features can be taken similar to
measuring distances on a map but topographical relief in images is similar to pictures (not
quantifiable). The shading is due to differences in observed reflected light, not direct height
measurements. Unlike AFM, SEM cannot be used to quantify the height of surface
structures or obtain information related to surface forces.
Optical Microscopy images a sample surface by observing the reflected and refracted light
directed through a series of lenses. The lateral resolution of optical microscopy is
significantly higher than SEM and AFM. Optical microscopy has a limited focus depth since
the lenses have a focal point, not a focal plane. Images of samples with large height steps
often have areas out of focus due to the inability to bring all heights into focus
simultaneously. By comparison, AFM provides unambiguous measurement of step heights,
independent of reflectivity differences between materials.
2. Nano Roughness
This is to be completed individually.
1.
Read the company profile and the memo from Kerry Prior that follows.
2.
On your answer sheet, answer the following questions.
a. List as many stakeholders as you can think of who may be impacted by the
deliverable your team has been asked to create. For each stakeholder, explain the
relationship between the stakeholder, the problem, and the deliverable.
b. Your solution will be implemented in the context described here and potentially in
other contexts. Describe issues (minimum five) that might arise for stakeholders when
your generalizable solution is implemented.
EGR 115 – Fall 2013
c. Consider your list of stakeholders. Who is the direct user of the deliverable your team
is being asked to create?
d. In a few sentences and in your own words, what does the direct user need? (Remember
to describe the deliverable, its function, the criteria for success, and the constraints.)
e. Consider the immediate problem as described and the sample data provided. Describe
at least two ideas you have for why this problem might be complex to solve.
Company Profile – Liguore Laboratories
Liguore Laboratories is an emerging technology company founded in 1996 to develop
nanostructured materials that improve performance and extend the life of coated orthopedic and
biomedical implants. The coating of orthopedic implants, such as joint replacements, is
undertaken with the aim of either increasing the wear resistance of the implant materials or
providing an implant surface that increases the biocompatibility of the implant with the
surrounding host bone. This increase in biocompatibility leads to formation of new bone around
the implant resulting in better fixation and improved long-term performance of the replacement
joint. Our company produces coatings for biomedical devices such as artery stents, bone screws,
fixation devices, and bone spacers.
Liguore Laboratories utilizes surface coating techniques to apply a full range of bioactive
coatings to orthopedic and biomedical implants manufactured by several global manufacturers.
The coatings include titanium, hydroxyapatite, alumina/titania, gold, calcium phosphate, and
other alloys. Our company has met and exceeded all industry and health standards for the United
States and Europe.
One of our more recent developments is the use of gold to coat artery stents. The Liguore
Laboratories materials research team found that gold, when heated, makes a smooth surface
coating for implants. The stents coated with lower roughness gold possess more biocompatibility
than stents coated with stainless steel.
Liguore Laboratories has assembled a talented group of scientists and engineers who possess an
in-depth understanding of the processes available for synthesizing the end product. They consult
regularly with leading biomaterials scientists, cell biologists, and clinical researchers within the
global community to develop innovative products that meet the clinicians' needs.
Liguore Laboratories is on the cutting edge of technology in the biomedical coatings industry.
Our mission is to create medical device coatings that provide performance and durability.
EGR 115 – Fall 2013
INTEROFFICE MEMO: LIGUORE LABS
TO:
NANOSURFACE ENGINEERING TEAM
FROM:
KERRY PRIOR, VICE PRESIDENT OF RESEARCH
RE:
SURFACE ROUGHNESS
Liguore Labs is very interested in the innovations of biomedical science. New research pertaining to
coatings for artificial hip replacements could represent a new venture for our company. Recently, a
physicist from University of Alabama, Birmingham named Dr. Yogesh Vohra accidentally produced
smooth diamond. When making synthetic diamond crystals in a laboratory, the gas reactor sprang a
small leak and let air into the mixture. Nitrogen from the air reacted with the carbon of the diamond. The
array of diamond created was smooth and adhered very easily to metal. Because diamond is durable, it
makes a very good candidate for coating artificial hip replacements. The current coatings wear down or
loosen from constant use after about 10 years, which could mean more surgery for the recipient. The
diamond coating is projected to last around 40 years, which would improve the comfort and health of the
patient.
Liguore Laboratories would like to expand our product line to include diamond coatings for hip joints. The
research laboratory is working on replicating the smooth diamond coating. In order for our materials
research team to know whether their production process is working (achieving the desired level of
smoothness), they need a quick and easy-to-use procedure to quantify the roughness of the nanoscale
diamond coatings produced in the lab.
Since we have experience with gold coatings and have many AFM images and data sets available, your
team can use these to develop a procedure to quantify the roughness of new coatings. Your team will be
provided with three atomic force microscope (AFM) images and associated data for gold coatings that we
have produced in our artery stent research lab. These images and data are described in the attached
Background Information attached. Your team needs to create a repeatable procedure using these images
and data as a reference to quantify the roughness at the nanoscale. Your team also needs to apply your
procedure to the AFM gold images and data. With this procedure in place, our materials research team
will be able to quickly quantify the roughness of the diamond coating samples as they are produced.
In a memo to my attention, please include your team’s procedure for quantifying roughness of the
nanoscale material using the AFM images and data. For this first iteration, provide results of
applying your procedure to the AFM gold image and data Sample C only. Please be sure to include
your team’s reasoning for the each step, heuristic (i.e. rule), or consideration in your team’s procedure.
Thank you for your team’s efforts in this endeavor. The expansion of our product line is an important
venture for Liguore Laboratories. I appreciate your prompt attention to this assignment.
Kerry Prior
Attached: Background Information
Background Information:
The two images on this page are images of smooth diamond from Dr. Vohra’s lab.
Figure 1a is a top-view image of the diamond. Figure 1b is a 3-dimensional side-view
EGR 115 – Fall 2013
of the same sample. The color bar on the right indicates the height of the diamond
surface.
Remember that:
μm stands for micrometers (1 μm = 10-6 m)
nm stands for nanometers (1 nm = 10-9 m)
Å stands for Angstroms (1 Å = 10-10 m)
Figure 1a. Top-view AFM image of smooth diamond.
Figure 1b. Three-dimensional AFM image of smooth diamond.
EGR 115 – Fall 2013
AFM Images: (AFM data courtesy of Purdue Nanoscale Physics Lab)
The three images below (Samples A, B, and C) are top-view images of gold that are provided
for use in developing your team’s procedure for quantifying roughness. The colorbar on the
right indicates the height of the gold surface. These images are generated from AFM data
which consists of the cantilever’s (X,Y) location and local height as the cantilever is drawn
over the surface of the sample. For instance, the first few and the last few data points for
Sample A would be:
WSxM file copyright Nanotec Electronica
WSxM ASCII XYZ file
X[µm]
Y[µm]
Z[Å]
0.000000
0.011742
0.023483
….
…..
5.976517
5.988258
6.000000
0.000000
0.000000
0.000000
675.345
671.311
667.278
6.000000
6.000000
6.000000
332.301
343.649
372.94
These height values can be arranged into an array and then translated into color values (in
this case grayscale values) so that the data can be visualized. The total number of
(X,Y,height) data points to generate a complete image can be quite large - for Sample A it is
262,146. Your team is provided with a slice of each of the three data sets so that you do not
have to handle such large data sets (which could crash your computer) but still get give you a
sense of the data.
Three AFM data files are available for your team to use to as a reference when developing
your procedure. The filenames are indicated with the images below. In the Excel file, you
will find two worksheet tabs:
 goldSampleX_view100%: is a slice of the height data arranged in an array
according to the (X,Y) locations (the X,Y locations are noted across row1,columnA,
respectively, in µm). Cells in which the height data are stored (in Å = angstrom) are
conditionally formatted for grayscaling so that the image appears when the
spreadsheet is zoomed to 10%. This sheet is set to view at 100% so that you can see
and use the height values.
 goldSampleX_view10%: is identical to goldSampleX_view100%, but the view is set
to 10% so that you can view the image slice. Note that the image slice constructed in
Excel is the bottom portion of each of the images below rotated 90 degrees.
EGR 115 – Fall 2013
Sample A
goldSampleA.xlsx
Sample B
goldsampleB.xlsx
EGR 115 – Fall 2013
Sample C
goldSampleC.xlsx