Biomedical Engineering Reference
In-Depth Information
patterns.to.be.created..The.separation.between.transfer.ribbon.and.receiving.substrate.is.
typically.>50.μm..A.short.separation.distance.reduces.the.areal.drift.that.would.otherwise.
result.in.imprecise.printing.
13.2 Laser Direct-Write Variations
Laser. direct-write. development. in. the. past. two. decades. has. led. to. many. variations.
of. the. basic. patterning. tool.. Strict. deinitions. of. different. varieties. of. laser. direct-
write. have. not. been. established,. and. many. experimental. setups. do. not. it. well. into.
a. category,. or. are. described. as. a. unique. mode. of. transfer.. It. is. important. to. note. the.
speciics. of. each. setup,. and. the. commonalities. present. in. the. mechanism. of. transfer..
Additionally,.laser.direct-write.provides.one.more.notable.advantage.over.many.other.
printing.methods:.they.are.all.noncontact,.and.so.avoid.one.major.source.of.contamina-
tion.(Wu.et.al..2003).
Each.type.of.laser.direct-write.technology.listed.above.relies.on.the.same.fundamental.
mechanism.of.transfer.(Schiele.et.al..2010)..All.use.transparent.ribbon.supports.coated.on.
one.side.with.the.target,.a.pulsed.laser.that.energizes.the.matrix,.and.a.receiving.substrate.
prepared.for.receiving.the.transfer.material..The.laser.pulse.interacts.with.the.target,.which.
converts.optical.energy.to.mechanical.energy,.propelling.transfer.material.to.the.receiving.
substrate..Resolution.achievable.by.these.methods.is.on.the.order.of.a.few.microns.(Esrom.
et.al..1995)..There.are.minimal.variations.in.laser.direct.techniques,.which.center.around.
differences.in.the.ribbon.and.the.naming.of.the.technique.
13.2.1  LiFT
LIFT. utilizes. a. typically. metallic. ilm. for. absorption. and. conversion. of. laser. energy. to.
mechanical. energy. for. printing.. In. this. case,. the. ilm. is. both. the. target. and. the. transfer.
material,.and.is.thin,.sometimes.less.than.half.a.micron.(Bohandy.et.al..1986)..The.separa-
tion.between.print.ribbon.and.receiving.substrate.can.thus.be.very.low..Distances.less.than.
10.μm.are.possible,.and.a.smaller.separation.is.generally.preferable,.as.a.smaller.separation.
yields.better.resolution..The.transfer.occurring.in.LIFT.happens.via.a.process.of.ablation.
and.is.most.applicable.for.inorganic.materials,.but.it.will.not.be.a.subject.of.focus.for.this.
chapter.. Cells. or. other. fragile. materials. can. be. coated. or. suspended. on. top. of. the. metal.
layer.for.a.procedure.called.AFA-LIFT.
13.2.1.1  AFA-LIFT
AFA-LIFT.is.a.variation.of.LIFT.wherein.the.transfer.material.coats.the.top.of.a.sacriicial.
target. ilm,. which. is. chosen. for. its. high. absorption. coeficient. corresponding. to. the.
wavelength. of.the.laser.to.be.used..As.the.target.and.transfer.material. are.separate,.the.
target.can.be.a.metal.ilm.chosen.for.optimal.optical.interaction,.while.the.transfer.material.
can.be.a.cell.suspension.that.would.otherwise.suffer.damage.from.optical.interactions,.or.
not.be.suficiently.absorptive..The.thickness.of.the.absorbing.target.layer.should.be.thick.
enough.so.that,.in.combination.with.the.high.absorption.coeficient,.the.layer.is.suficient.
to. absorb. all. of. the. laser. pulse,. and. limit. damage. to. the. transfer. material.. Laser. pulse.
 
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