Nanodiamonds for Bioimaging and Therapeutic Applications - The Nanobiotechnology - page 556

The.third.type.of.color.center.that.has.been.produced.in.ND.with.high.concentration.is.
H3.(Wee.et.al..2009)..The.center.consists.of.a.nitrogen-vacancy-nitrogen.complex,.N-V-N,.
originating.from.the.A.aggregate.in.natural.diamond.(or.type.Ia.diamond),.which.typi-
cally.contains.1000.ppm.of.nitrogen.as.impurity.(Davies.1994)..When.excited.by.blue.light.
at. its. absorption. maximum. (470.nm),. the. H3. center. emits. green. luorescence. at. 530.nm.
with. a. luorescence. quantum. yield. close. to. 1. (Table. 25.1).. Similar. to. (N-V) − ,. the. center.
emits.exceptionally.stable.luorescence.with.neither.photobleaching.nor.blinking,.as.dem-
onstrated.very.recently.for.single.H3.in.52.nm.ND.(Hsu.et.al..2011).

25.2.2 Mass Production of FND

Vacancies.in.diamond.can.be.created.by.radiation.damage.with.high-energy.electrons,.
neutrons,.protons,.alpha.particles,.or.gamma.rays.(Campbell.et.al..2002)..Upon.thermal.
annealing.at.600°C.or.above,.the.vacancies.become.mobile.and.are.subsequently.trapped.
by.nitrogen.atoms.to.form.N-V.or.N-V-N.centers..Presently,.the.most.commonly.used.
damaging. agents. are. ∼2.MeV. electrons. generated. from. a. van. der. Graaff. accelerator.
and.∼3.MeV. protons. generated. from. a. tandem. particle. accelerator. (Acosta. et. al.. 2009)..
However,.both.accelerators.are.very.sophisticated,.costly,.and.not.easily.accessible,.which.
hampers.the.availability.of.FNDs..To.overcome.this.hurdle,.Chang.et.al..have.explored.
the. feasibility. of. using. a. medium-energy. helium. ion. beam. to. create. vacancies. in. NDs.
(Chang.et.al..2008b)..Figure.25.3.illustrates.the.experimental.setup.of.the.ion.beam.appa-
ratus.for.scale-up.production.of.FNDs.(Chang.et.al..2008b,.Wee.et.al..2009)..The.helium.
ions. are. generated. by. a. discharge. of. pure. helium. in. a. radio-frequency. ion. source,. and.
then.accelerated.to.40.keV.by.using.a.high-voltage.acceleration.tube..The.typical.current.
of.the.unfocused.ion.beam.is.7.×.10 12 .He + /cm 2 ,.which.are.two.orders.of.magnitude.higher.
than. that. of. the. 3.MeV. proton. beam.. The. bombarded. NDs. are. subsequently. annealed.
at. 800°C. and. inally. oxidized. in. air. at. 450°C. to. remove. surface. graphitic. structures. to.
become.brightly.luorescent.

Nanodiamond-coated
copper ribbon

Ion beam

HV
acceleration tube

Supply reel

RF
ion source

Take-up reel

Pump Pump Pump

Figure 25.3
(See companion CD for color insert.) .Schematic.of.the.experimental.setup.for.mass.production.of.FNDs.with.
a. medium. energy. ion. beam.. The. RF. ion. source. produces. helium. ion,. and. then. the. high-voltage. acceleration.
tube. accelerates. the. ion. to. bombard. the. ND. on. the. copper. tape.. (Reprinted. from. Diamond. Relat. Mater .,. 18,.
Wee,.T.-L.,.Mau,.Y.-W.,.Fang,.C.-Y.,.Hsu,.H.-L.,.Han,.C.-C.,.and.Chang,.H.-C.,.Preparation.and.characterization.
of.green.luorescent.nanodiamonds.for.biological.applications,.567-573,.2009..Copyright.2009,.with.permission.
from.Elsevier.)