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/