Resonant-Infrared Pulsed Laser Deposition of Organic and Biological Thin FilmsJ. S. Horwitz, J. A. Callahan, E. J. Houser and R. A. McGill

Naval Research Laboratory, Washington, D.C. 20375

D. M. BubbPhysics Department, Seton Hall University

South Orange, NJ 07079

R. F. Haglund, Jr and M. R. Papantonakis Vanderbilt University, Nashville, TN 37235

Bo Toftmann, Risø National Lab, Roskilde, Denmark

LPC WorkshopJefferson LabsMarch 19, 2003

Outline

• Organic PLD– UV– Infrared

• Polymers– Polyethylene Glycol– Polysiloxane– Morphology

• Organic Semiconductors• Biomaterials• Mid-Infrared Light Sources• Conclusions

Organic Films• Wet techniques available to form organic monolayers

– Self Assembled Monolayers (SAM’s)– Soft Lithography (stamping)

• Wet techniques available to form organic thick films– Spin cast– Ink jet– Screen printing

• What if you need more than a monolayer, but less than a micron?

• Conformal coatings?• Advantages of vapor deposition:

– Accurate thickness control (nm-scale)– Conformal– Multilayers– No solvent interactions

Pulsed Laser Deposition

Vacuum Chamber

ExcimerLaser

SubstrateTarget

UV Transparent Window

193 or 248 nm.1 to 2 J/cm2

Plume

Rotating target

Versatile thin films tool for complex multicomponent inorganic materials

• Shallow penetration depth of UV laser results in efficient vaporization and atomization of target material

• Atomic vapor “self assembles” on substrate surface

• Organic materials can not re-assemble from atomic vapor

4000 3500 3000 2500 2000 1500 1000 500-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

N=C=OOH

Abso

rban

ce (a

. u.)

W avenum ber (cm -1)

Spin Coated Film PLD

UV PLD of of PolyurethaneFTIR Spectra

Evidence for photochemical modification of polymer

UV PLD: Gel Permeation Chromatography of Polyurethane Films

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0

0.0

0.2

0.4

0.6

0.8

1.0

Starting Material

PLD film

Mw ~ 125kMw ~ 600

Inte

nsity

(a. u

.)

log(Mw)Apparent Mw of film is smaller than monomer!

• Technique separatesparticles by size in column

• Mw determinationis based upon hydrodynamic volume of polymer in solution

Polyurethane = Polytetramethylene etherpolyol +Dicyclohexylmethanediisocyantein the presence of 1,4 Butandiol

n = variable chain length in Polytetramethylene etherpolyol,

n2 = chain length of polymer

Aliphatic = high H to C ratio in polymer

Photochemical Decomposition

• UV irradiation leads to electronic excitation• Potential mechanism for thermally induced unzipping of polyurethane• In spite of chemical changes to polymer, film still functional in

application

UV-Pulsed Laser Deposition

• UV-PLD for organic materials has had limited success. – Reduce laser fluence to minimize photochemistry– Typically observe reversible and irreversible damage

• Photochemical production of monomer• Irreversible decomposition

• For organic materials, need to develop new techniques which minimize photochemical damage.

UV-MAPLE

RefrigeratedRotatingAssembly Substrate

Holder

Frozen MAPLE Target Matrix

Volatile Solvent

Chemoselective Polymer

UV Laser Pulse

Volatile Solvent is Pumped Away

Sub

stra

te

RefrigeratedRotating Assembly

Matrix Assisted Pulsed Laser Evaporation• Imbed organic in volatile, UV light-absorbing matrix (1-5%)

–Laser evaporate composite, volatile matrix is pumped away–Success with some polymers and biological materials

Improved Surface Morphology for MAPLE SXFA Films

Aerosol Spray Coated MAPLE Coated

The MAPLE Polymer Coating is Highly Uniform.

MAPLE of Enzymes: Glucose Oxidase (GOD)

Tran

smis

sion

(Arb

. Uni

ts)

180017001600150014001300Wavenumber (cm-1)

Glucose OxidaseFilm Grown by MAPLE

180017001600umber (cm-1)

xidase YSId Solutionration Method)

GOD mw ~ 160,000

Comparison of FTIR of GOD Films

Tran

smis

sion

(Arb

. Uni

ts)

150014001300Waven

Glucose OStandar

(Drop Evapo

• IR Spectra of Enzyme Films Show Similar Structure.• Deposited Enzyme Films Are Active.

UV-MAPLE Disadvantages

• Low deposition rate (good for 100’s Å)• Still possibility of significant photochemical

interactions with solvents– Chlorinated hydrocarbons good organic solvents for

polymers– Direct evidence for photochlorination in some systems

• Not a universal technique

Thermal descriptions of ablation process fail in cases where there is high vibrational excitation density.

Resonant-Infrared PLD

Reaction Co-ordinateStarting material Photochemical

Product

S0

S1

Starting material

S0

S1

Electronic excitation and photochemistry with UV

Ground state vibrational excitation with resonant IR

• For UV, excited electronic state can relax back to ground state photochemical product.

• Infrared excitation: less total energy deposited into system• Highly vibrationally excited organic vapor in ground electronic state

5001000150020002500300035004000Vibrational frequency (cm-1)

O-H, N-H Str

C=C, C=N-C-H Str

-C-H Str

C=OC=C, C=N

C-H BendC-H Bend (Out of plane)

Resonant Infrared PLD

• All organic materials have strong absorption bands in the mid-infrared• Basic science questions relate to energy transfer:

– V-V and V-T– Which modes lead to efficient vaporization? – Which modes lead to chemical/structural modification?

• Take advantage of matrix effects in infrared (water for biological materials).– Use laser to selectively excite solvent.– Energy transfer between excited solvent and solute

RIR-PLD of Polyethylene Glycol (PEG)FTIR Spectra

4000 3500 3000 2500 2000 1500 1000 500-0.20.00.20.40.60.81.01.21.41.61.82.0

3.4 µm CH stretch excitation

2.9 µm OH stretch excitation

Abs

orba

nce

(a. u

.)

Wavenumber (cm-1)

Films have same structure when exciting either C-H or O-H stretch

FTIR for film and starting material are exact match

2.90 µm

H O C

H

H

C

H

H n

3.4 mm

Comparison of ESI Mass Spectrum of PEG Films

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

020406080

100

020406080

100

Target

m/z

RIR-PLD λ = 2.9 µm

Rea

ltive

Inte

nsity

(a. u

.)

•No evidence for photochemical modification in

MW~1500

Wavelength Dependence on Deposition RateFor Polyethylene Glycol

0 5 10 15

0

50

100

150

200

250

300

Dep

ositi

on R

ate

ng/(c

m2 *m

acro

puls

e)

Macropulse Fluence (J/cm2)

2.90 µm 3.45 µm

1 2 3 4

0

2

4

6

8

10

Macropulse Fluence (J/cm2)

Dep

ositi

on R

ate

ng/(c

m2 *m

acro

puls

e) 8.96 µm

H-(O-C-C-)n

H H

H H

Strong evidence for mode specific behavior

Mode Specific Behavior ?

4000 3500 3000 2500 2000 1500 1000 500-0.20.00.20.40.60.81.01.21.41.61.82.0

3.4 µm C-H stretch excitation

2.9 µm O-H stretch excitation

Abs

orba

nce

(a. u

.)

Wavenumber (cm-1)

Polyethylene Glycol

• O-H band is weakest absorption, but generates the largest deposition rate: How important is intermolecular attraction?

• O-H band has largest penetration depth.

Increasing Photon EnergyIncreasing Deposition Rate

8.96 mm C-O excitation

RIR-PLD Polymers

Fluoropolyol

OHO

R R

O

RR

OHO

R R

O

R R

n

R = CF3

Si O

OH

CH3

CF3

CF3

n

SXFA

Polystyrene

H-(O-C-C-)n

H H

H H

Polyethylene Glycol

-(CF2)n-Teflon

Polyaniline

poly(DL-lactide-co-glycolide) (PLGA)

[Si (CH2)3]n

OHCF3

CF3

OHCF3

CF3

HCS3A2 Versatile technique which preserves chemical structure and function

NH-)1-yNHNN )y((

HC C

O

O C

O

O

CH3 n n'

CH2

-[H2C-CH-]n-

Electroluminescent polymers for OLEDs

Applications for RIR-PLDCantilevers used for Explosives Detection

Back Front

200 µm

• Strain based sensor REQUIRES coating only on one side

• RIR-PLD used to deposit 500 nm of SXFA • Successful challenge with simulant vapor• Device requirements can not be met by

any other organic film technology

Si O

OH

CH 3

CF3

CF3

n

SXFA

6 7 8 9 10 11 12Wavelength (microns)

Infrared Spectrum for RIR-PLE of DMNB

H3C

CH3

CH3

H3C N

O

O

N

O

O

Excitation at 6.45 µm(N-O Stretch)

Est. Desorption Threshold ~ 30-40 µj/cm2

Film

Target

• RIR-PLE rapidly evaporates DMNB and the collected material is spectrally identical to the starting material

DMNB

Film Morphology

• Applications require smooth films• What are relevant surface dynamics• Examine the influence of deposition conditions on

microstructure– Target Structure– Laser

• Wavelength, fluence, repetition rate

– Ambient– Substrate temperature (strain based devices need RT

deposition)

Polystyrene on Si Morphology:Effect of Substrate Temperature

20 µm

130 C~RT-110 C

Carbosilane on Si Morphology

RIR-PLD has highly forward directed plume, like PLD

Target

Substrate

Laser Vapor Trajectory

Particle TrajectoryAttenuator

Pulsed laser passive filter deposition systemUnited States Patent 5,458,686 Pique, et al. October 17, 1995

Significant improvement in film morphology

Application for RIR-PLDOrganic Semiconductors

• Materials for next generation “flexible” electronics– Light weight (plastic substrates)– Low cost (room temperature processing) – Wearable and disposable

• FOM for organic semiconductors– Intrinsic mobility (1-10 cm2v-1s-1)

• One of the most critical problems to be solved is how to process the material in thin film form – Few techniques are capable of casting thin films of polymers– Grain boundary scattering limits electron mobility– Need a technique which offers control of thin film microstructure to improve

mobility

Spectra for RIR-PLD Polyanaline

500100015002000Wavenumber

Film

Target

Abs

orba

nce

(a.u

.)

• Insoluble in all organic solvents (only formed as a film by chemical or electrochemical polymerization on surface)

• Preservation of chemical and electronic structure• This will be the first report of successful vapor deposition of

material as thin film

Absorption maximum at 420 nm

CHEMISTRY OF MATERIALS 6 (5): 671-677 MAY 1994

RIR-PLD

NHNN )y(( NH-)1-y

Application for RIR-PLDBiological Thin Films

• Applications for Biomaterials in Thin Film Form Include:– Microfluidic biosensors and biochips– Advanced drug coatings – “Smart” materials such as pH or temperature sensitive

polymers)– Direct drug deposition (proteins, DNA, etc.).– Co-deposition of DNA/biopolymers for gene therapy

RIR-“MAPLE” of Biological MaterialsProteins

• 2.9 µm excitation (H2O)• Biotinylated bovine serum albumin (BSA) film deposited

through a shadowmask• After deposition, the slide is washed fluorescently tagged

streptavidin which binds to BSA• Green emission evidence for presence of BSA (results similar

to UV-MAPLE)

DNA-based Vaccines• In DNA-based vaccines:

–Pieces of DNA take up residence in a cell (gene addition, gene replacement).

–New DNA causes the cell to manufacture a protein that protects against disease (easier to make DNA than protein)

addition

replacement

• Two main research areas:– What DNA?

– How to deliver DNA to cells

– Coated needles

– Coated nanoparticles

Unsuccessful by UVPLD

RIR-“MAPLE” of DNA (λ = 2.9 µm)

Marker (low end 500 bp, high end 1200 bp)

Control (non-laser deposited DNA)

Low E, Laser DepositedDNA at λ = 2.9 µm

IR Matrix excitation as energy at 2.9 µmabsorbed by water, not DNA

• Electrophoresis of eluded salmon DNA shows replication of broad MW

RIR-PLD Film

Circular

• Replicated NarrowMW distribution

pBluescript II sk(+)

Supercoiled circular

Mid-Infrared Lasers• Free Electron Lasers (FEL)

– High power, high rep rate, tunable laser

• Is there something unique about FEL?– Complex Vanderbilt pulse structure (long macropulses, ps

micropulses)

• Other less expensive mid-infrared lasers– Er:YAG (fixed, 2.94 µm)

• Biological materials• Any O-H containing organic material/matrix

– OPO, OPA (> $60K )

• FEL – Industrial processing of materials

Influence of Macro-pulse Structure on Deposited Films

Shutter

M

MPockel Cell

M

Polarizer50 cm fl BaF

P(base) = 10-6 torr

P(dep) =10-3 torrIR Beam

Macropulse width100 ns to 4 µsec

350 ps1 ps wide micropulseM Filter

0

50000

100000

150000

200000

250000

2 3 4 5 6 7 8

Deposition Rate for short macropulseDeopsition Rate for full macropulse

Freq

uenc

y Sh

ift

Pulse energy (mj)

Influence of Macro-pulse Width on Deposition Rate of Polystyrene (3.4 microns)

•Non-linear dependence of deposition rate on fluence•Deposition rate independent of macropulse structure

0.4 nm/min

50 nm/min

1000150020002500300035004000

RIRPLD of SXFA

Er:YAG

FEL

Wavenumber

22.4 24 25.6 27.2 28.8Time

Starting MaterialEr:YAGFEL

Comparison of FEL and Er:YAG

• Er:YAG (2.94 µm): 5 Hz, 100 ns FWHM, 30 mJ/pulse

• To first order, see no difference in FEL vs Er:YAG for polymeric materials

2.94 µm

IR Spectra for SXFA GPC for HC2SA2

polymer

monomer

Bio Comparison of FEL and Er:YAG

• Significant differenced observed in biological materials (RIR-MAPLE)

– No bands observed in DNA electrophoresis using Er:YAG

– Matched macropulse fluence to Er:YAG – sample thermally damaged by 100 ns pulse

Summary• RIR-PLD has been demonstrated as a versatile tool to

form thin films of organic and biological materials. • Currently investigating fundamental aspects of

resonant infrared laser/material interactions as they relate film growth

• Explore the science necessary to apply technique to thin film materials needed for:– Chemical sensors– Lightweight, low cost, flexible electronics– Applications for DNA coatings

PLD Working Group• NSF Partnerships for Innovations (NSF Solicitation

03-521)• Partnerships among academe, state/local/federal and

private sector (15-25 awards, $600K for 2-3 yr) • Planning meeting at NRL Feb. 2003

– J. Horwitz, A. Pique, R.A. McGill, M. Kelly, R. Haglund, J. Greer, D. Bubb

– A. Reilly, J. Fitzgerald, K. Schriver• NSF requires lead PI needs to be “senior institutional

administrator (academic dean or higher)– Dennis Hall, Vanderbilt University

• Government, Academic and Industrial Participants– NRL, JLab, College of W&M, UVA, Seaton Hall, Industry

(IBM)• Goal: State of the art PLD machine for FEL research

PLD Working Group (cont.)• Machine focus on organic materials (low temperature

processing, lower cost) upgradeable to high temperature processing– Applications to chemical sensors (required industry interest)– Cooling of target required for organics

• Like Aerospace porgram, construction of 2 general purpose PLD machines by PVD Products – Vanderbilt –Small machine for survey work (2” diameter max)– Jefferson – Industrial Scale (larger area)

• Need to define machine specifications• Letter of Intent sent to NSF February 27, 2003• Proposal due April 9, 2003• Any and all suggestions appreciated!

PVD-PLD …Coming to User Labs Soon!http://www.pvdproducts.com/