Biomedical Engineering Reference
In-Depth Information
transfer.also.correspond.to.the.smallest.transferred.volume..Laser.F1.induced.heating.of.a.
metal.target.ilm.results.in.explosive.boiling.of.the.adjacent.liquid,.which.produces.a.gas.
pocket.that.expands.and.drives.transfer.of.target.material.(Craciun.et.al..2002;.Duocastella.
et.al..2009;.Brown.et.al..2011)..Momentum.and.viscous.forces.cause.a.thin.jet.to.form.upon.
collapse. of. the. bubble.. AFA-LIFT. using. a. polymer. target. ilm. yields. a. similar. jet;. how-
ever,.the.process.of.formation.is.different..Below.the.threshold.energy,.the.target.ilm.will.
absorb.the.laser.and.trap.decomposition.gases.forming.a.pressurized.pocket.in.the.ilm..
Time-resolved.images.of.the.ilm.reveal.that.conditions.for.transfer.correspond.with.the.
threshold. for. pocket. rupture. (Brown. et. al.. 2011).. Larger. laser. beam. diameters. can. also.
cause.transfer.via.an.unruptured.pocket,.wherein. surface.tension. becomes.a.signiicant.
factor..Unruptured.pockets.created.with.spot.sizes.similar.to.those.used.for.metal.ilms.
and.ruptured.pocket.transfer.do.not.provide.a.suficient.impulse.to.fully.detach.the.trans-
fer. material.. In. the. case. of. a. metal. ilm,. the. propulsion. is. mainly. derived. from. vapor-
ized. transfer. material.. Metal. fragments. often. accompany. the. ejected. material,. and. can.
cause.contamination,.as.well.as.cause.the.nucleation.of.bubbles.within.the.jet..These.cause.
damage.or.inconsistent.coverage..Polymer.ilm.rupture-based.jets.avoid.these.secondary.
bubbles,.but.still.involve.high.temperatures.and.pressures,.so.damage.to.the.transfer.mate-
rial.is.unavoidable..Unruptured-pocket-based.jets.are.never.exposed.to.the.hot.gasses,.and.
may.provide.the.most.gentle.AFA-LIFT.approach.for.transfer.of.delicate.and.thermal.sensi-
tive.materials..At.very.high.luences,.it.has.been.seen.that.the.gas.pocket.bursts,.producing.
splashing.on.the.receiving.substrate.(Young.et.al..2001).
In.MAPLE.DW,.the.laser.pulse.interacts.with.a.sacriicial.target.matrix.containing.the.
transfer.material..The.laser.energy.causes.explosive.ablation.of.the.layer.on.the.print.rib-
bon..When.MAPLE.DW.was.conducted.with.barium-zirconium.titanate.(BZT).powder.in.
an.alpha-terpineol.matrix,.the.ablation.response.was.signiicantly.delayed..Although.95%.
of.the.laser.pulse.is.absorbed.in.the.irst.200.ns,.the.irst.visible.ejection.of.material.does.
not. occur. until. around. 300.ns. later.. This. is. due. in. part. to. the. particulate. content. of. the.
matrix,. and. to. the. viscosity. of. the. alpha-terpineol.. The. BZT. particles. absorb. the. major-
ity. of. the. laser. energy. and. the. heat. diffuses. to. vaporize. the. alpha-terpineol. matrix.. The.
expansion.of.the.bubbles.is.slowed.by.the.viscosity.of.the.matrix..Time-resolved.micros-
copy. performed. with. the. MAPLE. DW. technique. has. revealed. several. transfer. regimes,.
depending.on.luence.(Chrisey.et.al..2002)..About.150.ns.laser.pulses.of.355.nm.wavelength.
caused. the. development. of. a. pluming. regime,. a. jetting. regime,. and. a. below. threshold.
regime. in. a. BaTiO
3
. nanopowder. and. alpha-terpineol. matrix.. These. regimes. are. energy-
dependent.(Lewis.et.al..2006)..At.high.luences.of.0.65-0.065.J/cm
2
,.a.vapor.pocket.formed.
as.in.the.aforementioned.AFA-LIFT.technique;.however,.the.energy.was.suficient.to.cause.
the.ejected.material.to.overcome.viscous.and.adhering.forces,.expand,.and.form.a.diffuse.
plume..Lower.luences.of.0.039-0.026.J/cm
2
.produce.a.jet,.where.the.vapor.pocket.collapses.
and.the.jet.remains.coherent,.although.breaking.into.droplets.after.5.μs.and.over.a.range.of.
100.μm..These.timescales.and.distances.are.much.less.than.those.experienced.in.the.trans-
fer.process,.implying.that.coherent.jets.are.maintainable..Fluences.lower.than.0.026.J/cm
2
.
were.insuficient.for.causing.transfer..Close.to.this.threshold,.formation.of.a.vapor.pocket.
is.seen,.but.the.energy.is.not.high.enough.to.cause.full.detachment.of.any.transfer.material.
The. formation. of. a. pressurized. gas. bubble. is. central. to. the. AFA-LIFT. and. MAPLE.
DW. schemes. of. transfer.. It. is. also. important. to. note. for. transfer. purposes. that. due. to.
the. extremely. short. pulses. that. are. universally. used,. heat. loss. is. negligible. during. the.
timescales. of. interest. as. heat. diffusion. does. not. have. enough. time. to. exert. a. signiicant.
effect.. FEM. reveals. several. characteristics. of. the. transfer. process.. A. higher. coating.
