YAN W U , A N D R E W W O E R P E L , A N D L E E FA R I N A

D E P T. O F E N G I N E E R I N G P H Y S I C S

U N I V E R S I T Y O F W I S C O N S I N - P L AT T E V I L L E

O C T O B E R 1 0 , 2 0 1 4

P R E S E N T E D T O C O N F E R E N C E F O R M I D W E S T

N A N O T E C H N I C I A N P R O G R A M S

Teaching Nanofabrication Process

Design and Diagnosis using Nano-

sphere Lithography

Overview of MSNT 3940: Principle and

Applications of Nanotechnology A broad spectrum of topics

• Nano-physics, Nano-chemistry, Nano-biology, Material Science

• Applications: solar cells, water purification, drug delivery, nano-

transistors four-year degree in MSNT.

Lab centered course emphasizing on hands-on experience

• Fabrication skills Lithography

Thin film deposition using sputtering and thermal evaporator

Wet and dry etching

Chemical synthesis of nanostructure

• Characterization tools Scanning electron microscope (SEM)

Atomic force microscope (AFM)

Stylus profilometer

Contact angle goniometer

The Challenge: How do we teach design and problem solving in a nanotechnology course?

Motivation

• ABET accreditation process needs design and

problem solving content in engineering courses

• Nanotechnology advances rapidly. We need to

teach students skills, not just knowledge.

• Process design and diagnosis skills are needed

in both industry and academia

One of our efforts: Nanosphere Lithography Lab

Nanosphere Lithography (NSL): the concept

• Creating arrays of nano-sized metal cone structures from thin film

deposition and template masking with nanospheres.

• Applications: surface enhanced Raman Spectroscopy, catalyst for

subsequent etching or growth

AFM image of NSL result, Andrew Woerpel, 2014

Nanosphere Lithography: the realization Things that can go wrong in an undergraduate teaching lab:

Problem with application

of the spheres: clumped

up and poorly packed

spheres

Problem with metal

deposition: too much

metal seals the space

between spheres

Problem with sphere

removal: left-over

spheres and regions with

complete metal removal

We can figure out all the process parameters and hand down a process

‘recipe’ to students

Or we can let the students take the responsibility of process design and

diagnosis, but not without help…

What makes NSL process successful?

Hydrophilic substrate helps the spheres spread evenly.

• Ways to prepare substrates: wet cleaning with

chemicals, surface treatment with O2 plasma, UV

Ozone cleaner

• Ways to check the wettability of a surface: water

contact angle.

Definition of contact angle

Hydrophilic surface,

contact angle <90° Hydrophobic surface,

Contact angle >90°

What makes NSL process successful?

Directional metal deposition process, film thickness should

be around one fifth the diameter of the sphere.

• Thin film deposition tools: evaporator vs. sputterer

• To check film thickness: stylus profilometer

lower vacuum pressure

longer mean free path

more directional deposition

What makes NSL process successful?

Lift-off the spheres without attacking the interface between

metal and substrate.

• Ways to lift-off the spheres: organic solvents

(acetone, toluene) vs. mechanical exfoliation (Scotch

tape)

• To check the completeness of sphere removal and

final the product: SEM, AFM

SEM image showing nanospheres SEM image showing surface after nanosphere removal

Lab structure

Scheduled in the later half the semester when

students already have the experience with all the

tools needed in the lab

One lecture before the lab to introduce the concept

Assign homework of designing the fabrication process

Two lab sections, each lasts two hours, for students

to complete the process

During the lab, students work in teams (2-3 students

per team

One discussion unit after the lab

Student Work Example I

Process

• UV Ozone cleaning 10 min,

contact angle after cleaning 14º

• Spin coating of nanospheres:

1000 RPM for 30 sec

• Thin film deposition: sputtered

chrome,

• Lift off: Acetone and sonic

agitation

Quote from the report:

“This is a good showing of the difference between the nanospheres that are

lifted off and those that were left behind. If I were to repeat this experiment I

would use higher speeds and longer time for the nanosphere spin coating ”

Student Work Example II

Quote from the report:

“Overall, the patterns were successfully deposited onto the coverslip.

However, the sharpness was only marginally acceptable. This issue could

have been alleviated by increasing the deposition time”

Process

• UV Ozone cleaning 30 min,

contact angle after cleaning 8º

• Spin coating of nanospheres:

3000 RPM for 20 sec

• Thin film deposition: sputtered

chrome, 46nm in thickness

• Lift off: Scotch tape

Student Work Example III

Quote from report:

“I learned that a lot of things do not work: (1) Acetone, IPA, and water

cleaning; (2) Sputtering deposition; (3) Sonication in toluene”

Process

• O2 plasma cleaning 30 sec,

contact angle after cleaning

less than 4º

• Spin coating of nanospheres:

2000 RPM for 30 sec

• Thin film deposition:

evaporated aluminum, 150nm

in thickness

• Lift off: Scotch tape

ABET Course Outcomes

Primary outcomes

• To develop an understanding of the connections between science

and engineering knowledge and nanotechnology

• To be able to identify, formulate, and solve engineering problems

using nanotechnology principles

• To be able to interpret data from instruments and to conduct

experiments in nanotechnology.

• To be able to use nanotechnology techniques and tools

Secondary outcomes

• Communication skills

• Team work skills

• Life-long learning skills

• Ethical, environmental, and societal context of nanotechnology

Assessment from the instructor

• About a third of the students can successfully design

and carry out Nanosphere Lithography

• Most students can correctly identify the step of the

process that causes problem, but sometimes miss the

real reason for failure

Student work: samples from different runs

Student Self-assessment

From the students’ self assessment (on the scale of 5)

• I learned how to interpret data from instruments and

how to conduct experiments in nanotechnology. (4.78)

• I can use nanotechnology techniques and tools.

(4.89)

• I am able to communicate technical information

effectively, both orally and in writing. (4.78)

• I can function in multi-disciplinary teams. (4.56)

Student work: samples for comparing the effect of film thickness

Summary

• It is import to integrate teaching design and problem

solving skills in nanotechnology education.

• Nanosphere lithography lab can be a platform for

teaching process design and diagnosis

• The concept is simple to explain

• A variation of nanofabrication techniques and

characterization tools are needed

• The result is easy to check