using heatable afm probes for the nanolithography of ......ibm’s millipede large arrays of probes...

Using Heatable AFM Probes for the Nanolithography of Polymers, Nanoparticles, and Graphene

Paul Sheehan

U.S. Naval Research Laboratory

SEM: Heatable Cantilever

Heating is controlled by passing a current through the cantilever

Heatable Cantilevers [King Group, UIUC]

Infrared Microscopy

Tmax: 1200 °C

Diamond Coating @ ADT

Rcurv: ~ 20 nm

Fletcher et al., ACS Nano (2010) 4:3338

Nanoscale Modification with Heatable Probes

Direct Deposition

Indirect Deposition

Heatable probes can deposit material directly, deposit material indirectly by mixing with a carrier polymer, or can chemically convert existing films through heating.

Graphene Lithography

Direct Deposition = thermal DPN

25 °C

57 °C 98 °C

122 °C

OPA Indium

Materials Deposited to date Small Molecules OPA—functionalize ITO, glass electrodes [APL (2004) 85: 1589] Anthracene—conducting molecule 1,2,4,5-tetrakis(phenylethynyl)benzene—Carbon Nanotube Precursor

Metal Indium—used the tip as a nanoscale “soldering iron” [APL (2006) 88: 033104]

Polymers Conductive—PDDT [JAP (2010) 107: 103723], MEH-PPV Insulators—Mylar, polyethylene, PMMA, PEI Piezoelectric—PVDF, PVDF-TrFE Electroluminescent—PFO Temperature Responsive—pNIPAAM [Soft Matter (2008) 4:1844]

Many different materials may be deposited using the tip as a nanoscale soldering iron. Polymers work particularly well and are ordered during deposition.

Robust deposition

Total Writing time = 286 s 1.5 s for long lines 0.5 s for short line We can write > 3 mm without reloading tip. Over 5000 structures written with a single tip.

120 lines of the conductive polymer PDDT Deviation within

column < ~5%

Deposition modulated using a second control system

1 m

PDDT on SiO2 written in

•UHV (1 x 10-10 Torr)

•Height = ~ 20 nm (8 MLs)

•Linewidth = ~ 150 nm (fwhm)

1.0

0.5

0.0

10.05.00.0

1 ML

4 MLs

20 m/s

8 m/s

0 2.6 m

Adjusting the probe speed enables PDDT to be written layer by layer.

In-situ Polymer Nanofabrication in UHV

<height> (nm)

Because the technique uses heat alone, it is vacuum compatible.

submitted, Beilstein J. of Nanotech.

Control over Orientation

•Rastering the tip over an area combs the polymer creating even greater order.

•Each bundle of polymer strands is 73±4 nm wide (~190 stands) which is comparable to the tip’s radius of curvature.

tip direction

A single pass with a very dull tip

Rastering a rectangle with a sharp tip

17 nm

0 1 2 3

<height> (nm)

2 µ

m

Substrate

2.6

nm

Lee et al., JACS (2006) 128: 6774

Shearing the polymer between the tip and the substrate aligns polymer along the tip path.

Laracuente et al., J. Appl. Phys. (2010) 107: 103723

New Properties—Temperature Responsive Polymers

Ahn et al, Adv. Mater. (2004), 16, 23-24, 2141

• Poly(N-isopropylacrylamide), or PNIPAAm, is a stimulus-responsive polymer that shifts from hydrophilic to hydrophobic when its temperature is increased above 32 °C

• PNIPAAm brushes can nonspecifically bind biomolecules, proteins, and bacteria when collapsed (T > 32 °C) and release them when rehydrated state (T < 32 °C).

• The large dimensional changes hinder accurately positioning an adsorbed molecule

10 nm

Can we retain the surface free energy shift while

maintaining dimensional stability?

New Property of deposited pNIPAAM

Lee et al., Soft Matter, 4, 1844 (2008)

The surface aligned pNIPAAM deposited via tDPN can shift its surface energy while maintaining its dimensions.

0 10µm

0

20nm

height: 2.37±0.1 nm

0

20nm

0 10µm

height: 2.47±0.1 nm

40°C

H2O

2

3°C

H2O

Same Height

Adhesion Forces

Typical force-distance curve

23°C

40°C

Adhesion force

Protein Binding on deposited pNIPAAM

0

3

6

0

3

6

0

3

6

C B

A

µm5.5

y-a

vera

ge

heig

ht

(nm

)

A

0

1

2

3

4

5

6

7

Avera

ge H

eig

ht

(nm

)

// Init

ial

Rin

se

Rin

se

Ne

utr

avid

in

BSA

Co

ntr

ol

23°C

40°C

23°C 23°C

40°C

23°C

Lee et al., Soft Matter, 4, 1844 (2008)

pNIPAAM deposited via tDPN can reversibly capture and release proteins while maintaining its dimensions.

Fluorescence of FITC-labeled neutravidin bound to micrometer scale pNIPAAM patterns

Indirect Deposition

Current Limitations nP alignment—it’s rare that they are well-aligned Heterogeneity—hard to deposit different materials side by side Compatibility—solution processing vs. UHV Registration—often difficult to align with external features Flexibility—techniques are often wed to a single chemistry which limits the choice of substrate, nP, and polymer

The State of the Art for Nanoparticle Deposition

Self Assembly anisotropic labeling, charge

DeVries et al., Science (2007) 315: 358

50 nm

200 nm

Warner et al., Nature Mat. (2003) 2: 272

Soft Templates DNA, viruses, diblock polymers, etc

Hard Templates pits, tubes, etc.

Bai et al., J. Mat.Chem (2009) 19: 921

Indirect Deposition—Polymer Nanocomposites

O 2 plasma

Nanocomposite flows from heated tip

to surface

use as-is

Nanoparticle Assembly Nanocomposite Lee et al., Nano Letters (2010) 1: 129

1 µm

Nanocomposites

140 nm

polyethylene + quantum dots

Fluorescence

P(VDF-TrFE) + Alq3

2 µm

40

nm

Topography

Fluorescence

w/ nP w/o nP

MFM

PMMA + Fe3O4 nPs

w/ nP w/o nP

Many different polymers, nanoparticles, and substrates were used.

Nanoparticle Assemblies

Generally, the particles disperse through the polymer matrix…

1 µm

SEM

Au nPs

O2 Plasma

10 nm

Aligned nanoparticle assemblies

O2 plasma

SEM

250 nm

250 nm

200 nm

aligned Fe3O4

nanoparticles

SEM

Particles aligned during deposition

By controlling the solubility of the nanoparticle in the polymer, it is possible to have the polymer align the nanoparticles into chains. The particle may be functionalized to remove the effect.

Direct-Write Graphene Nanoribbon Circuitry

Graphene Nanoribbon Circuitry

Unlike graphene, graphene nanoribbons (GNRs) have band gaps which are needed for low-power switchable components. The electronic and magnetic properties of GNRs may be controlled by chemically modifying their surfaces and edges. These GNRs can serve as active and passive components in graphene circuitry. High thermal conductivity enables high densities of devices

Areshkin et al., Nano Lett (2007) 7:3253

The State of the Art in Graphene Nanoribbons

Shatter graphene using ultrasound

Dai group @ Stanford ion/ioff ~ 100,000 no ability to place or shape ribbon, broad width distribution, low yield

E-beam lithography

Kim group @ Columbia, Avouris @ IBM

ion/ioff ~ 2,500 @ low T

line edge roughness: 3-5 nm; fails @ 20 nm

Several approaches to obtain Graphene Nanoribbons (GNRs)

Slice open carbon nanotube

Tour group @ Rice (also Dai group)

ion/ioff : 100-1,000 no placement, rough edges, oxidation

Geometric versus Chemical Isolation

Lee et al. Nano Lett. (2011) 11: 5461

Fluorination with XeF2 [Robinson@NRL]

*Robinson et al. Nano Lett. (2010) 10: 3001

Fluorination with XeF2 generates two stoichiometric graphene fluorides (CF, C4F)

Chemical Isolation advantages—mobility

The edge terminates at sp3 carbons covalently bound to fluorine rather than at a collection of sp2 and sp3 hybridized carbons bound to a variety of oxygen rich functional groups as would be left by oxygen plasma etching.

-40 -30 -20 -10 0 10 20 30 400

1

2

Dirac Point Voltage

Rsheet (k

)

Vg

3. hydrazine

reduced

1. initial

2. GNR

0

5

10

15

cou

nts

Produces ribbon edges that are robust and chemically well-defined The carrier mobility in the final device is 95±14% that of the starting material


Chemical Isolation advantages—reversible

-40 -30 -20 -10 0 10 20 30 400

1

2

3

4

5

reduced

Rsheet (k

)

Vg

3. hydra

zine

1. initial

2. GNR

Because the carbon skeleton is left in place, one can expose the film to hydrazine, reducing all the material back to graphene and enabling one to start over. The resistance goes from open circuit (>~100,000x) back to a 3x higher than the original

Once can reverse the fluorination for rewriteable electronics


-50 -40 -30 -20 -10 0 10 20 30 40 500.0

0.5

1.0

1.5

2.0

2.50.0

0.5

1.0

1.5

2.0

2.5

Rsh

eet (

k)

Vg

Geometric Isolation

Rsh

eet (

k)

Chemical Isolation

Chemical Isolation advantages

The intact graphene sheet prevents adsorbates from intercalating under the GNR and modifying its electronic performance

After 30 min

After 2 weeks

Device Response after Vacuum Anneal


Thermal Reduction

Heat from the scanning probe pyrolyzes the GO reducing it back towards graphene

Wei et al., Science (2010) 328: 1373

Variable Reduction

Hotter tips reduce the GO more as shown by friction images. Conductivity may be varied by 10,000x.

Wei et al., Science (2010) 328:1373

Large Films—Epitaxial Graphene on SiC @GA Tech

Epitaxial graphene may be oxidized globally and reduced locally

che

mical

oxid

ation

SiC

graphene

SiC

graphene oxide

Generic approach: TCNL on fluorographene

Reduction by heated probe could be performed in N2 environment. After reduction, the height

of 300-nm wide reduced line was ~0.7 nm lower and produced lower friction than the

surrounding fluorographene. These results are comparable to the performance of graphene

oxide. Resistance = 2.0 MΩ

0 200 400 600 800 1000

0

1

2

3

4

5

6

7

8

he

igh

t (Å

)

X (nm)

-1.5E-08

-1.0E-08

-5.0E-09

0.0E+00

5.0E-09

1.0E-08

1.5E-08

-0.010 -0.005 0.000 0.005 0.010

Vg= -40V

Vg= +40V

0

20

40

60

80

100

120

140

160

-50 -40 -30 -20 -10 0 10 20 30 40 50

VSD

I SD

R

sheet (k

)

Vg

To Do—the nanoscale breadboard

IBM’s Millipede

Large arrays of probes already exist and enable parallel writing for wafer scale patterning

We are beginning the task of integrating this different materials into a nanoscale breadboard where multiple materials such as polymer, nanoparticles, and graphene nanoribbons can be integrated into working devices.

www.zurich.ibm.com

Collaborators and Funding

Heatable Cantilevers @ UIUC

Prof. William King

Zhenting Dai

Patrick Fletcher

Johnny Felts

Graphene growth and Processing

E. Riedo (GA Tech)

Jeremy Robinson

Rory Stine (Nova Research)

Scott Walton

Mira Baraket

Funding Office of Naval Research DARPA

30

DARPA

tDPN Minchul Yang (NRL USPTO) Woo Kyung Lee GNR Writing Zhongqing Wei (NRLCAS) Debin Wang (GA TechLLNL) Woo Kyung Lee Michael Haydell (USNA a ship somewhere in the Pacific Ocean)

Theory Daniel Gunlycke Tom Reinecke

• extra slides

Focusing Mechanism

Precipitation on Tip Shearing the nPs results in an entropic penalty for solubilizing the nPs. The nPs fall out of solution and condense onto the tip

Pure polymer aligned by tip

Hydrodynamic focusing The fastest region is the center which will entrain the nPs

17 nm

Width Control

•Nanoparticles condense onto the tip during deposition

•Nanoparticles cluster when the tip is still but align when the tip moves

•Miscibility affects alignment

6 nm high

100 nm

138 nm high

nPs cluster when tip

stalls for 2 s

AFM

150 100

50 0

5 µm

8 4 0

5 µm

O2 plasma

30 min

etch

PMMA + Au nanoparticles

What is Graphite Oxide?

• Single-layer GO sheets can be prepared chemically by oxidizing pristine graphite via the Hummers method, the Brodie method, or the Staudenmeier method.

• The graphite oxide is soluble in water and a stable aqueous dispersion of GO can be readily prepared via mild sonication.

The color of synthesized GO solid is much lighter due to the loss of electronic conjugation brought about by the oxidation.

H2SO4 NaNO3

KMnO4 dry

sonicate in H2O GO solid

Stankovich et al., J. Mat. Chem. 16 (2006) 155

WS Hummers and RE Offeman, JACS 80 (1958) 1339

on a SAM

on Mica

Single-layered GO Sheets on Various Surfaces

Single-layer GO sheets can be dispersed on commonly used substrates such as mica, silicon, HOPG, and self-assembled monolayers (SAMs)

GO/mica (Height)

4 n

m

400 nm

2

1

0

-60

3

0 m

V

400 nm

3 n

m

200 nm

1

0

-7

10

mV

200 nm

after writing a diamond before writing

Writing Areas

Rastering the tip allows areas to be filled in.

600 nm

0 1 2 3

-0.2

0.0

0.2

0.4

0.6

0.8

He

igh

t (n

m)

Distance (µm)

Counts

0.4

1±

0.1

6 n

m

The measured height change was 0.41±0.16 nm.

Large Area Films—Epitaxial Graphene on SiC

All carbon electronics will require large area films Epitaxial graphene is produced by Si desorption at high temperature in vacuum -Si is more volatile than C Very different surface morphology for C vs. Si face

400nm

SiC after H2 @ 1600°C

6.67

0.00

Si face

C face

Four Probe Electronic Measurements

Line Measurements

Graphene nanoribbons have been tested.

No GNR

With GNR

On to graphene monolayers…

Extend process to large area monolayers of graphene*

Cu

PMMA

Si Si

Low E Plasma**

*Li et al. Science (2009) 324: 1312

graphene

friction topography

1 µm

~65 nm wide

**Baraket et al., APL (2010) 96: 231501

SEM topography

Thermal Patterning of perfluorographane

3.0µmNot the same pattern, but the same patterning conditions:

~500 °C and 15 scans @ 7µm/s

2 µm


-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7-50-40-30-20-10

01020304050

curr

ent

(nA

)

V


Perfluorographane

Fluorination is a robust and flexible route to further chemical functionalization of graphene

Bannerjee et al. Adv. Mater. (2005) 17: 17

Layer-by-Layer Height Control

The hot polymer anneals during deposition. This allows us to deposit PDDT layer-by-layer

The 2.6 nm height agrees with XRD of a PDDT SAM film (Prosa, Macromolecules ’92)

Substrate

2.6

nm

Yang et al. JACS (2006) 128: 6774

0 1 2 3 4 5 6 0

5

10

15

20

Hei

ght

(nm

)

distance (µm)

500 nm 500 nm 500 nm 500 nm

µm s

0.1 0.5 1 5 10 50 0.1 vtip

Tip

Path

PDDT monolayer

Depositing Nanoparticles

Particle / Macromolecule

Size

(nm)

Carrier

Polymer Substrate Wtotal/

WnP

Aluminum Triquinone ~0.9 P(VDF-TrFE) SiO2 1x

zinc diethyldithiocarbamate ~1.2 P(VDF-TrFE) SiO2 1x

CdSe-ZnS core-shell 2-4 PE SiO2 1x

Dodecanethiol functionalized silver 2-4 PMMA SiO2 n/m

Dodecanethiol functionalized gold 2-4 PDDT

PMMA

SiO2,

SAM

~2x

1.9x

HMDS-functionalized iron oxide ~6 PMMA SiO2 2.3x

iron oxide 6.5±3.0 PMMA SiO2

Au, mica

36x

We have deposited metal, semiconductor, magnetic, and optical nanoparticles.

Polystyrene/GNRs

The sheet resistance of the hybrid GNRs does increase below ~70 nm. Whether this

is due to the opening of a bandgap or other effects is currently being determined.

Smallest linewidths are currently 33 nm fwhm.

0 50 100 150 200 250 300 350 400 450 500 550 0

500

1000

1500

2000

She

et R

esis

tance (

/square

)

GNR width (nm)

Writing Lines

We first started writing onto flakes that had been cast onto silicon oxide.

The topographical width of the line is ~25 nm but could be narrower with sharper tips.

closer view of the X average profile of trench

200nm

aver

aged

x (nm)

he

igh

t (Å

)

0 40 80 120 160

0

0.5

1

1.5

2

2.5 25 nm

Wei et al., Science (2010) 328:1373

after writing a diamond before writing

Writing Areas

Rastering the tip allows areas to be filled in.

600 nm

0 1 2 3

-0.2

0.0

0.2

0.4

0.6

0.8

He

igh

t (n

m)

Distance (µm)

Counts

0.4

1±

0.1

6 n

m

The measured height change was 0.41±0.16 nm.

Large Films—epiGraphene ►Riedo@GaTech

Epitaxial graphene may be oxidized globally and reduced locally

che

mical

oxid

ation

SiC

graphene

SiC

graphene oxide

Four Probe Electronic Measurements

Polystyrene deposition

-40 -30 -20 -10 0 10 20 30 40 50 600.0

0.5

1.0

1.5

2.0

2.5

PS spincoat

base deviceRsh

eet (

k)

Vg

Polystyrene was chosen because of •easy melt processability •hydrophobicity •resistivity (10-16 S/m ) •it does not dope graphene as shown by an absence of a shift in the VD when it is spin coated onto the base device

Heated Tip

Deposited Polymer

polystyrene The PS line width was controlled from 60 to 300 nm by controlling writing speed with the narrowest lines being achieved at write speeds of 40 µm/s. Lines of polystyrene were written at ~250°C just above its melting point with diamond-coated heated probes.

Fluorination with XeF2



using heatable afm probes for the nanolithography of ......ibm’s millipede large arrays of probes...

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