Biomedical Engineering Reference
In-Depth Information
solution,.different.surface.roughness.and.size.of.nanostructures.may.result. 55 .Branching.
of.nanostructures.at.the.base.is.another.issue.with.the.process,.and.pore.diameters.of.less.
than.20.nm.can.exhibit.irregular.patterns. 53,54 .Block.copolymers.(BCPs).are.another.tech-
nique. to. fabricate. template-based. nanostructures. for. LSPR. applications.. Nanostructures.
such.as.spheres,.cylinders,.and.lamellae.are.all.dependent.on.the.composition.and.chain.
structure.of.the.polymers. 59 .The.features.can.range.from.5.to.50.nm.as.a.function.of.the.
BCP.molecular.weights. 59 .The.inal.self-assembled.nanoparticle.pattern.is.dependent.on.
the.BCP.domain.symmetry..Generally,.micrometer-scale.areas.are.achievable,.but.defects.
can.exist.at.grain.boundary.edges. 60 .Examples.of.defect-free,.large-area.BCP.domains.on.
templated. and. lithographically. deined. surfaces. have. been. demonstrated, 60,61 . with. both.
methods. using. a. combination. of. top-down. and. bottom-up. processes.. The. high. cost. of.
extreme.ultraviolet.interferometric.lithography.limits.wide-scale.application.of.the.latter.
process, 60 .while.e-beam.lithography.of.grooves.combined.with.plasma.etching.is.required.
for.the.former. 61
5.3.2.4   Nanosphere Lithography
Nanosphere.lithography.(NSL).is. a.templating. method.using. monolayer. or.double-layer.
colloidal. nanoparticles. for. submicron. and. nanometer-scale. patterns.. Preparation. tech-
niques. include. electrostatic. deposition,. self-assembly,. drop. casting,. spin. coating,. and.
evaporation, 53,62 .forming.a.hexagonal,.close-packed.monolayer.on.the.substrate.with.control-
lable.size,.shape,.and.interparticle.spacing. 63 .After.metal.is.deposited.onto.the.nanoparticle.
array.by.thermal,.e-beam,.or.pulsed.laser.deposition,.the.NSL.templates.are.then.removed.
by.burning.off.at.temperatures.or.chemical.dissolution.with.organic.solvents. 53 .The.advan-
tages.of.NSL.include.low.cost,.high-throughput.compatibility.with.many.materials,.and.
the.capability.of.producing.well-ordered.arrays.on.different.substrates. 64 .Nanostructures.
such.as.nanopillars, 65 .nanohole.arrays, 66 .nanowire.arrays, 67 .nanobowls, 68 .nanotriangles, 63 .
nanorings, 69 . and. nanocrescents 70 . have. been. fabricated. successfully. for. LSPR. applica-
tions..However,.NSL.suffers.from.several.disadvantages..First,.formation.of.colloidal.par-
ticles.into.a.mask.has.limited.geometries.due.to.the.hexagonal.close-packed.formation. 71 .
Although.a.modiied.NSL.with.varying.gaps.can.be.fabricated,.the.process.would.involve.
etching,. ion. beam. techniques,. or. spin. coating. prior. to. pattern. transfer. 71,72 . Different. gap.
sizes.affect.the.tunability.of.substrate.plasmonic.resonances, 73 .so.it.is.important.to.have.
lexibility. with. adjusting. the. gap. between. particles.. Since. the. size. of. nanoparticles. and.
gap.distance.between.holes.or.features.are.interdependent,.control.over.substrate.features.
has.additional.constraints. 71 .Finally,.structural.defects.such.as.nanosphere.polydispersity,.
dislocations,. vacancies,. polycrystalline. domains,. or. local. polystyrene. (PS). or. latex. bead.
disorder.are.often.transferred.to.the.new.substrates,.leaving.limited.defect-free.areas.(10.
to. 100. μm 2 ). 74 . The. NSL. method. has. been. modiied. in. multiple. ways,. including. transfer-
ring.monolayers.via.submersion.in.millipore.water, 75 .liquid-gas.interface.self-assembly, 74a .
angle-resolved.NSL, 76 .shadow.NSL.with.annealed.PS,.and.fabricating.dimers. 8a
5.3.2.5   Oblique Angle Deposition and Glancing Angle Deposition
The.OAD.method.is.a.physical.vapor.deposition.at.a.glancing.angle.(>75°).of.the.substrate.
normal.with.respect.to.the.incoming.vapor.direction.(Figure.5.3a),.causing.a.geometrical.
shadowing.effect.that.leads.to.a.preferential.growth.of.nanorods.on.the.substrate.in.the.
direction.of.deposition.(Figure.5.3b.and.c)..More.speciically,.in.the.initial.stages.of.ilm.
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