Dr. Richard A. WyskIndustrial & Manufacturing Engineering Department

Pennsylvania State University

CNT-Based Nano-Scale Fabrication: Creating Commercially Viable Nano-Manufacturing

Dr. Chuck ZhangDr. Ben Wang

Industrial & Manufacturing Engineering DepartmentFlorida State University

Presentation Outline

Background and Motivation

Review of NanoEM Process

Research Objectives

Experimental Setup and Investigations

Challenges

Conclusions and Future Work

Review of Nano-manufacturing Processes

Current Nano-fabrication Techniques:

Focused Ion Beam (FIB), Femto-Second Laser, Scanning

Probe Microscope (SPM), UV Lithography

Limited Resolution and Production Rate

Work only for SILICON and POLYMERIC materials. (Malshe et

al., 2005)

Electro Machining: Electro-Beam Machining (EBM), Electro-

Chemical Machining (ECM), Electro-Discharge Machining

(EDM)

Excellent for producing micron-sized features

Ability to generate 3-D features

Limiting Feature: Conventional Electrode Size ~ 20μm

Review of NanoEM Process

Non-contact process with small forces on both the

electrode and the workpiece.

Based on the thermoelectric energy created between a

workpiece and an electrode submerged in a dielectric

medium.

Workpiece + Electrode → separated by ‘spark-gap’

Pulsed discharge → Material Removal by Melting,

Evaporation and chemical reactions

Among other factors, Size and Form of the machined

feature depends primarily on properties of the electrode

such as electrode size, conductivity and strength.

Ignition Plasma formation Melting and evaporation

http://nmrc.yonsei.ac.kr/

Review of Nano-EM Processes

Feature Size(nm)

ElectrodeMaterial

PositioningSystem

OperatingEnvironment

WorkpieceMaterial

MaterialRemoval

Rate(nm3/s)

U of Kentucky

(Shreve & Vallance, 2004)

200 Tungsten STM Air Au -

U of Maryland(Gomez 2005) 150 Tungsten

STM +InertialMotor

Air/Vacuum

Au, Si3N4

-

U of Arkansas(Malshe et al. 2005) 10 Pt-Ir

STM(nano)

Oil Au (111) 141

Current ResearchPreliminary Results 30

CarbonNanotube

AFM &nano-stage

AirAu,

HOPG 700-8000 (HOPG)

Research Objectives

Use of Carbon Nanotubes as Electrodes

Non-Vacuum Environment – Commercial Nano-

stage instead of AFM

Range of materials including Si, Au and HOPG

Commercialization of the process

Targeted Feature Size: ~10nm

Targeted Material Removal Rate: 1000nm3/s

Foundation for creating $ 0.10 nano features

SiHOPG

Au

Power Source

Experimental Setup

Preliminary Experimental Setup using AFM:

AFM Tip Holder

NanoEm Experiments: STM tip

Etched tungsten tip

Resulting feature on Au (~ 200 nm)

U. of Kentucky

U. of Maryland

Etched tungsten tip

Holes using STM tip

NanoEM Experiments: Buckypaper Electrode

Experimental Setup:

Buckypaper Electrode

Silicon wafer with gold pattern surface

Buckypaper after EDM Buckypaper before EDM

NanoEM Experiments: Buckypaper Electrode

40V single pulse 100ms

50V single pulse 100msGap ~ 2 um

Holes using Buckypaper Electrode

Holes using Buckypaper Electrode(contd.)

Gap ~ 10 um

50V single pulse 100ms

Holes using AFM Tip

Typical hole diameter: ~100nm, distance between hole: 500nmPositioning error is due to open-loop piezo

-10V, 50ms (50 % duty ratio), 1000 times on HOPG surface

Holes using AFM Tip (contd.)

50ms, 1000times on Cr/Au film (after washing and blowing)

Metal-coated (Cr/Au) AFM tip, contact mode

Diameter: 130 nmDepth : 10 nm

Diameter : 100 nmDepth : 4 nm

-15V

-10V

AFM Tip with MWNT Attachment as Electrode

Solution processedRaw MWNT sample

• AFM was used to approach tip to the MWNT surface from top

• Cr/Au(10 nm/30 nm) coated AFM tip

• MWNT dispersed in surfactant (AC electric field 10 Vpp, 10 MHz )

• Too many MWNT surfactant remnant

AFM Tip with MWNT Attachment as Electrode (contd.)

~ 5V

• HOPG substrate• Commercial nanotube tip (CNTEK, MWNT

probe)

Holes using AFM Tip + MWNT Electrode

Before After

HOPG surface

10V, 100ms single pulse

AFM Tip with a

MWNT

Slots using AFM Tip + MWNT Electrode

6V 7VWidth : 38nmLength : 160nm

Width : 44 ~ 58nmLength : 400nmHOPG

Nanotube contact substrate with angle and bended

10nm60nm

MWNT Tip after Discharge

After discharge

Before discharge

Nanotube burn out?Or blasted away by force?

Some of the Challenges…

Plethora of uncertainties associated with the actual material

removal mechanism:

Discharge in nanoEM very sensitive to the environment (especially

moisture). Electrodes wear out immediately.

NanoEM process → Complex energy transport requiring multiple

levels of models of plasma generation + interaction with the surface.

Experimental Investigations: Surface response for ambient n-EM is

quite different from mere creation of craters, the main micro-EDM

mechanism → Need for Simulation Modeling.

At nano-level, sublimation from the surface, rather than melting and

evaporation, may be responsible for the material removal process.

Conclusion and Future Work

So near yet so far ! Experimental Investigations show the NanoEM

Process to be technologically feasible. Yet, lot of further research is

desired.

A preliminary simulation model is currently being built in ANSYS

using Thermo-electric and Thermo-elastic Analysis.

Further technological assessment includes detailed metrics

concerning feature size/variation/location, material removal rates,

electrode life, aspect ratio, profile of features, as well as the impact of

voltage and pulse characteristics on performance.

References

A.P.Malshe, K.Virwania, K.P.Rajurkar and D.Deshpande, 2005, ”Investigation

of Nanoscale Electro Machining (nano-EM) in Dielectric Oil”, CIRP Annals –

Manufacturing Technology, 54(1), pp.175-178.

S.M.Shreve and R.Vallance, 2004, “Nano-EDM Utilizing Etched Tungsten

Nanoprobes & Modulated Electrical Fields”, Lab Poster presented at The

Ninth Annual International Symposium for Magnetic Bearings,

www.engr.uky.edu/psl

J.G.Park, C.Zhang, R.Liang and B.Wang, “Nano-machining of highly oriented

pyrolytic graphite using conductive atomic force microscope tips and carbon

nanotubes”, 2007, Nanotechnology, 18(40).

Research by Dr. Gomez, University of Maryland, College Park.

http://www.cartoonstock.com/newscartoons/cartoonists/cgo/lowres/cgon188l.jpg

Thank You!