Nanotechnology-unit 1.ppt

Nanotechnology notes for the preparation with definition and scope along with history and application in various sectors like security

1. Introduction
Thedefinitionofnanotechnologyisbasedonthe
prefix“nano”whichisfromtheGreekwordmeaning
“dwarf”.Inmoretechnicalterms,theword“nano”means
10
-9,
oronebillionthofsomething.Forcomparison,a
virusisroughly100nminsize.Thewordnanotechnology
isgenerallyusedwhenreferringtothingswiththesizeof
0.1to100nm,beyondthatlimit,isreferredtoas
microtechnology.

2. Nanotechnology :Nanotechnology ismakingand
manipulatingmaterialsandstructuresthatare
smallerthan100nminsize.
Nanobiotechnology :Itistheamalgamation of
biotechnology and nanotechnology
Itisatechnology for thedesign,
characterization,productionandapplicationof
structures,devicesandsystemsbycontrolling
shapeandsizeatnanometrescale.
Definition and Scope of Nanotechnology

4. THE NANOMETER SIZE SCALE

5. History of Nanotechnology
1959-RichardFeyman:Statedthefamous
statement ”Thereisplentyofroomatthe
bottom”.Describedaprocesstomanipulate
individualatomsandmolecules thatmightbe
developedusingprecisetoolstobuildandoperate
anothersetofsmallermoleculestotherequiredscale
1965-GordonMoore:Predictedthatthenumberof
transistorsthatcouldfitinagivenareawoulddouble
every18monthsforthenexttenyears(thisbecamea
realitywithpentium4containingabout40,000,000
transistors)
1974-NTaniguchi:definedthetermnanotechnology
as“Nanotechnologymainlyconsistsoftheprocessing
ofseparationconsolidationanddeformationof
materialsbyoneatomorbyonemolecule.

6. 1986 –EricDrexler promoted the
technologicalsignificanceindepth and
popularisedthesubject.
1980’s–Nanotechandnanosciencegota
boostwiththeinventofSTMandAFM
History of Nanotechnology contd …

7. Persons involved in Nanotechnology research
RalphMerkle:Nanotechnologytheorist
RobertFeritas:Nanomedicinetheorist
SumioLijima:Discovererofnanotubes
Richard Smalley, HarryKroto-Discovererof
Buckminsterfullerene
GerdBinnig,HeinrichRohrer-Inventorofscanning
tunnelingmicroscope
PhaedonAvouris-Firstelectronicdevicemadeoutof
carbonnanotubes
DavidTomanek –Tounderstandfundamentalproperties
ofnanostructuredmaterialsusingadvancednumerical
techniques.

8. Applications of Nanomaterials

9. Applications of Nanomaterials Contd..

10. Applications: Security
Securityisabroadfield,coveringeverythingfromthe
securityofourborderstothesecurityofour
infrastructuretothesecurityofourcomputernetworks.
Superior,lightweightmaterialsforarmedforcesandair
crafts
Quantumcryptography—cryptographythatutilizesthe
uniquepropertiesofquantummechanics—willprovide
unbreakablesecurityforbusinesses,government,and
military.
Chemicalsensorsbasedonnanotechnologywillbe
incrediblysensitive—capableofpinpointingasingle
moleculeoutofbillions.
Nanometals,nano-sizedparticlesofmetalsuchas
nanoaluminum,aremorechemicallyreactivebecause
oftheirsmallsizeandgreatersurfacearea.(Stronger
explosives)

11. Applications: Healthcare
Thelab-on-a-chipiswaitinginthewingsto
analyzeapatient’sailmentsinaninstant,
providingpoint-ofcaretestinganddrug
application.
Newcontrastagentswillfloatthroughthe
bloodstream,lightingupproblemssuchas
tumourswithincredibleaccuracy
Nanotechnologywillaidinthedeliveryofjustthe
rightamountofmedicinetotheexactspotsof
thebodythatneeditmost.(Noveldrugs)

12. Promiseof Nanotechnology

13. Materialsdesignedatthemolecularleveltotake
advantageoftheirsmallsizeandnovelproperties.
Thetwomainreasonswhymaterialsatthenanoscale
canhavedifferentpropertiesareincreasedrelative
surfaceareaandnewquantumeffects.(Quantum
mechanics (QM)isasetofscientificprinciples
describingtheknownbehaviorofenergyandmatter
thatpredominateattheatomicandsubatomicscales).
Theuniquepropertiesofthesenanomaterialsgive
themnovelelectrical,catalytic,magnetic,mechanical,
thermal,orimagingfeaturesthatarehighlydesirable
forapplicationsincommercial,medical,military,and
environmentalsectors.
Nanomaterials

14. The most current nanomaterials could be organized
into four types:
i.Carbon Based Materials
ii.Metal Based Materials
iii.Alluminosilicates (Imogolite)
iv.Calcium phosphates (Hydroxyapatite)
v.Dendrimers
vi.Nano carriers

15. Nanomaterials have unique properties

16. CARBON BASED
NANOMATERIALS
Composed of carbon,
commonly taking the
form of hollow spheres,
ellipsoids, or tubes.
NANOTUBES
BUCKYBALLSFULLERENES

17. METAL BASED
NANOMATERIALS
Include quantum dots,
nanoshells, nano gold
probes and metal
oxides particles.
Changing their size
changes optical
properties.
NANOSHELLS
QUANTUM DOTS
MAGNETIC
NANOPARTICLES
NANOPARTICL
E PROBES

18. DENDRIMERS
These are globular,
highly branched
nanostructures with
numerous chain ends,
tailored to perform
specific chemical
functions.

19. NANO CARRIERS
Combine nanoparticles
with other nanoparticles or
with larger, bulk-type
materials to enhance
physical properties.
MICELLES
LIPOSOMES
POLYMER
NANO
PARTICLE

20. Alluminosilicates nanomaterials (Imogolite)
Some naturally ocurring or synthetic clays such as imogolite are
inorganic nanotubes with mesophore.
Imogolite forms tubular structures.
The external tube diameter of imogolite has been shown to be
approx 2.5nm and the tubes are several micrometers long.
The tubes exist in a high degree of order as self alligned bundles
Applications: In the field of catalysis support, ceramic filter, humidity
contolling building materials
Calcium phosphates nanomaterials (hydroxyapatite):
Hydroxyapatite and other related calcium phosphates have been
studied as implant materials in orthopedics and dentistry because of
their excellent hard and soft attachment, biocompatibility and ease
of formation

21. AllotropesofCarbon:
Carbon allotrope = The different molecular
configurations, that pure carbon can take.
•Diamond
•Graphite
•Amorphous carbon
•Fullerenes
•Carbon nanotubes
•Aggregated diamond nanorods
•Glassy carbon

22. THE DISCOVERY
HarryKroto,RichardSmalleyandRobertCurl
attemptedtocreatehigh-temperatureconditionsin
thelaboratory.Theyvaporizedgraphitewitha
powerfullaserinanatmosphereofheliumgas.
Graphite
Helium gas atmosphere

23. Theresult…
When theyanalyzed theresultingcarbon
clusters,theyfoundmanypreviouslyunknown
carbonmolecules.Thesevariedinsize,but
themostcommon molecule contained 60
carbonatoms.Thestructurewasextremely
stableandtheyconcludedthatonlyasphere-
likemolecule couldachievethislevelof
stability.
Theyworkedoutthattheonlygeometric
shapethatcouldcombine60carbonatoms
intoasphericalstructurewasasetof
interlockinghexagonsandpentagons
Naming: Buckminster fullerene
, Nobel prize for discovery

24. WHAT AREFULLERENES?
Fullereneareafamilyofcarbonallotropes,inthe
formofahollowsphere,ellipsoid,tubeorplane.
Sphericalfullerenesarealsocalledbuckyballs,
andcylindricalonesarecalledcarbonnanotubesor
buckytubes.
Thefullerenewasdiscoveredin1985byRobert
Curl,HaroldKrotoandRichardSmalleyatthe
UniversityofSussexandRiceUniversity,who
nameditafterRichardBuckminsterFuller,whose
geodesicdomesitresembles.

25. Buckminster fullerene got its name after Richard
Buckminster Fuller who is the architect of geodesic dome
found in this picture…

26. STRUCTURAL VARIATIONS ON
FULLERENES
Buckyballclusters:smallestmember isC20
(unsaturatedversionofdodecahedrane)andthe
mostcommonisC60;
Nanotubes:hollowtubesofverysmall
dimensions,havingsingleormultiplewalls;
potentialapplicationsinelectronicsindustry;
Megatubes:largerindiameterthannanotubes
andpreparedwithwallsofdifferentthickness;
potentiallyusedforthetransportofavarietyof
moleculesofdifferentsizes
Polymers:chain,two-dimensionalandthree-
dimensionalpolymersareformedunderhigh
pressurehightemperatureconditions

27. PROPERTIES
Physical structure
Fullerenecagesareabout7-15Angstromsin
diameter.Inatomic terms, theyare
enormous, butstilltheyaresmalleras
comparedtomanyorganicmolecules.
Theyarelargeclosed-cagecarbonmolecules
consistingofanumber offivemembered
ringsandsixmembered rings.Inorderto
makeaclosedcage,allfullerenemolecules
shouldhavetheformulaofC20+m,wherem
isaninteger.
Stability
Theyarequitestable,breakingtheballs
requirestemperatures ofover1000degree
C.Atmuchlowertemperatures, fullerenes
willsublime.

28. Solubility
Fullerenesaresparinglysolubleinmany
solvents.Common solvents forthe
fullerenes include aromatics, such as
toluene,andotherslikecarbondisulfide.
Superconductivity
Intercalationofalkali-metalatomsinsolid
C60leadstometallicbehavior.In1991,it
was revealed that potassium-doped
fullerenesbecomessuperconducting at18K.
Sincethen,superconductivity hasbeen
reportedinfullerenedopedwithvarious
metals.
Properties contd …

29. THE PRODUCTION OF FULLERENES
The first method of production of fullerenes used laser
vaporization of carbon in an inert atmosphere, but this
produced microscopic amounts of fullerenes. In 1990, a
new type of apparatus using an arc to vaporize
graphite was developed in Germany by Kratschmer and
Huffmann.

30. •Thisproducesalightcondensatecalledfullerene
soot,whichcontainsavarietyofdifferentfullerenes.
•Thefullerenesarethenextractedbyavarietyof
differentsolventsofwhichtolueneisthemostwidely
usedbecauseofitslowcost,lowboilingpointand
relativelylargecapacityforcarryingfullerenes.
•Separationandpurificationhappensbycolumn
chromatography

31. ENDOHEDRAL FULLERENES
Endohedralfullerenesare
fullerenesthathaveadditional
atoms,ions,orclustersenclosed
withintheirinnerspheres.
Fullerenecompounds areair
sensitive,theoxygenpullsoutthe
extraatomsoutofthefullerene
lattice.Enclosureofanatominside
afullerenegivesitaddedstability.
Twotypesofendohedralcomplexes
exist: endohedral
metallofullerenes and non-
metaldopedfullerenes

32. Metallofullerenes
Whentheatomtrappedinsidethefullereneisametal,itiscalled
asmetallofullerene.
Metallofullerenesarecharacterisedbythefactthatelectronswill
transferfromthemetalatomtothefullerenecageandthatthe
metalatomtakesapositionoff-centerinthecage.
Theseanionicfullerenecagesareverystablemoleculesanddonot
havethereactivityassociatedwithordinaryemptyfullerenes.
Theyarestableinairuptoveryhightemperatures(600to
850°C).Common metalatomsincludelanthanum,yttrium,
scandiumetc.
Non-metal doped fullerenes
Whentheatomtrappedinsideisanonmetalsuchas
helium,neon,argon,kryptonorxenon,itiscalledasnonmetal
dopedfullerene.Inthesecompoundsnochargetransferofthe
atominthecentertothecarbonatomsofthecagetakesplace.
Thecentralatomintheseendohedralcomplexesislocatedinthe
centerofthecage.

33. Discovered by Professors at Rice University
It is C-60 structure(12 pentagonal and 20
hexagonal)
C
60 is the smallest fullerene molecule in
which no two pentagons share an edge.
It is also the most common in terms of
natural occurrence, as it can often be found
in soot.
The van der Waals diameter of a C60
molecule is about 1 nanometer(nm). The
nucleus to nucleus diameter of a C60
molecule is about 0.7nm.
Buckyballs
(Sphere-like allotropes of carbon)

34. InC60,hexagonsand
pentagonsofcarbonlink
togetherinacoordinated
fashiontoformahollow,
geodesicdome
BuckyBall ….
Desirable properties:
1.Theyexhibitahollowcage-likeshape
2.Theyareextremely stableandcan
withstandveryhightemperaturesand
pressures.
3.ThecarbonatomsofBuckyballscan
reactwithotheratomsandmolecules,
leavingthestable,sphericalstructure
intact.
4.Iftheyarecompressed andthen
releasedtheyspringbacktotheir
originalshape.Andtheybounceif
theyarehurledagainstahardsurface
suchassteel.
5.Fullerenesaresparinglysolublein
manysolvents.Common solventsfor
thefullerenesincludearomatics,such
astoluene,benzeneetc.

35. Applications
Fullerenescouldbeputtoworkastinychemical
sponges,moppingupdangerouschemicalsfrom
injuredbraintissue.Buckyballs,madesolublein
water,appearto‘swallow’andholdfreeradicals,
therebyreducingthedamagetotissue.
Buckyballsinminiaturecircuits:Scientists
compressed theBuckyballby15percent,
improvingelectricalconductivitybymorethan
100timescomparedtotheundisturbedmolecule.
Atinyelectroniccomponentlikethiscouldmake
miniaturecircuitsfeasible.

36. MoreApplications
Buckyballs behaving as'molecular ball
bearings'allowingsurfacestoglideoverone
another.
Buckyballcompounds withaddedpotassium
actassuperconductors atverylow
temperatures.
Becauseofthewaytheystack,Buckyballs
couldactasmolecular sieves,trapping
particlesofparticularsizeswhileleaving
othersunaffected.
UsingBuckyballstoimproveresolutionof
photocopies.Theyare1000timessmaller
thantheparticlesusedinconventional
photocopiermachines.

37. EvenMoreApplications
Buckyballsmaybeusedtodelivermedicines
tospecifictissuesandcells,suchasthose
thathavebeenattackedbyacertain
bacteria,protectingtherestofthebody
fromthetoxiceffects.
Administration of armed
Buckyballs intoatissue
throughamicrosyringe.The
deliverysystem willbe
incorporatedwithdrugsthat
combatviralattack.

38. Improved MedicalResonance Imaging(MRI)
contrastagentsandimageenhancers that
exploitthecarboncageofaBuckyballtoshield
patientsfromtheradioactivematerialsinside.
Due to their extremely resilient nature bucky
balls are debated for use in combat armor.
Bucky balls can be used as lubricants,
protective coatings.

39. CARBONNANOTUBES
Nanotubes are cylindrical
fullerenes.Thesetubesofcarbon
areusuallyonlyafewnanometres
wide,buttheycanrangefromless
thanamicrometer toseveral
millimetersinlength.Theyoften
haveclosedends,butcanbeopen-
endedaswell.
Theiruniquemolecularstructure
resultsinextraordinarymacroscopic
properties,includinghightensile
strength, high electrical
conductivity,highductility,high
resistancetoheat,andrelative
chemicalinactivity

40. Carbonnanotubesarelong,thin
cylindersofboundcarbonatoms,
about100,000timesthinnerthan
ahumanhair,andcanbesingle-
or multi-walled.They have
remarkable electronic and
mechanicalpropertiesthatdepend
onatomicstructureandmore
preciselyonthemannerinwhichthe
graphenesheetiswrappedtoforma
nanotube(chirality).Theycanbe
eithermetallicorsemiconducting
Boron-nitride nanotubes also show potential for similar applications.
BN nanotube. B atoms are in red, N atoms in blue
Nanotubes….

41. They are the strongest and stiffest materials on earth in terms of
tensile strength and elastic modules respectively
They are not nearly as strong under compression because of their
hallow structure , they tend to under go buckling when placed
under bending stress.
Multiwalled nanotubes precisely nested within one another exhibit
a strking telescoping property whereby an inner nanotube core
may slide almost without friction within its outer nanotube shell,
thus creating an atomically perfect linear or rotational bearing.
They behave as a excellent metallic or semi conductors depending
on the configaration.
All nanotubes are expected to be very good thermal conductors
along the tube exhibiting a property known as ballistic conduction
but good insulators laterally
Have no signs of toxicity
Properties

42. Carbon nanotube with metal-
semiconductorjunction
Structure of a multi-walled
nanotube
Nanotubes

43. Nanotubes classified
•Single-wall carbon nanotubes (SWCNTs) -
These are formed by the rolling of a single
layer of graphite (called a graphene layer)

44. Multiwall carbon
nanotube(MWCNT)
A multiwall carbon nanotube can
similarly be considered to be a coaxial
assembly of cylinders of SWCNTs.

45. Thejoiningoftwocarbonnanotubeswithdifferentelectrical
propertiesformadiode.
Usedascompositefibersinpolymerstoimprovemechanical,
thermalandelectricalpropertiesofthebulkproduct.
Duetotheirgreatmechanicalpropertiesofthecarbon
nanotubetheyfindtheirapplicationsinclothes,sportsgear
andspaceelevators.
Inelectricalcircuitsbecauseoftheiruniquedimensionstoan
unusualcurrentconductionmechanismtheymakethemideal
componentofelectricalcircuits.
Asavesselfordrugdelivery:Drugdosagetobeloweredby
localizingitsdistribution
Usedaselectrodesinbatteriesandcapacitors
Haveapplicationsinavarietyoffuelcellcomponents
Usedassuperstrongfiberswillhaveapplicationsininbody
armour,transmissionlinecables,wovenfabricsandtextiles.
Applications of carbon Tubes

46. Biomedical applications: Cells have been shown to
grow on bucky tubes appear to have no toxic effect.
The ability to chemically modify the sidewalls of
bucky tubes have been used for vascular stunts and
neural growth and regeneration.
Other Applications

47. What is a Nanoshell?
Nanoshells are optically tunable nanoparticles
that have a dielectric core and an ultra thin
metallic layer of the order of a few
nanometers as its shell.

48. Propertiesofgoldnanoshells
•Strongopticalabsorptionandyielda
brilliantredcolour.
•The opticalresponse ofgold
nanoshellsdependsontherelative
sizeofthenanoparticlecoreandthe
thicknessofthegoldshell.
•Byvaryingtherelativecoreandshell
thicknesses, thecolorofgold
nanoshellscanbevariedacrossa
broadrangeoftheopticalspectrum
thatspansthevisibleandthenear
infraredspectralregions.
Silica core
Gold
coating

49. Visual demonstration of tunability of metal
nanoshells
Nanobiotechnology and diseases

51. PropertiesofNanoshells
Coatingofcolloidalparticleswithshellsoffers
themostsimpleandversatilewayofmodifying
theirsurfacechemical,reactive,optical,
magneticandcatalyticproperties.
Functionalmaterialswithnovelpropertiescan
besynthesizedusingvariouscombinationsof
core-shellmaterialandbyvaryingshell
thickness.

52. OPTICAL PROPERTY
Metal Nanoparticles show optical absorption in the visible range
of the electromagentic spectrum and sometimes in the IR
Region.
Their absorption range is mostly from 300-800 nm.
Preferred core=Silica, shell=Gold
As mentioned earlier, the optical response of gold nanoshells
depends on the relative size of the nanoparticle core and the
thicknes of the gold shell.
By varying the relative core/shell thickness, there can be a
good change in color that spans across the broad visible and IR
spectral regions (Tuning)
The ability to tune nanoshells to a desired wavelength is critical
to in vivotherapeutic applications.
Human blood and tissue minimally absorb IR wavelengths of
light enabling us to therefore use an external laser to deliver
light to nanoshells either in a tumor or a wound.

53. SurfaceChemicaland
CatalyticProperties
Core-shell particles offer high surface area and
can be used as efficient catalysts.
Preferred core= titania, shell= Silica
Bulk Titania is thermally unstable and loses its
surface area readily.
But coating a thin layer of some other stable
oxide (such as silica) can greatly improve its
catalytic activity.

54. Stability of magnetic materials is important when
studying their magnetic properties.
To improve the surface characteristics and to protect
them from reacting with various species, they are
coated with inert material.
Silica is the best choice for such a purpose because it
forms stable dispersions, is not magnetic and does not
interfere with magnetic properties of the core.
Magneticmaterialsaresusceptibletoagglomeration
andshowanisotropicinteractions.
Athincoatingofsilicaisthebestwaytoprotectthem
fromagglomeration.
Magneticparticleswhencoatedwithsilicaare
suspended inmedium, isotropicinteractionsare
observed.
Magnetic Properties

55. Enhancement of thermal stability
Depressionofmeltingpointinnanoparticlesas
comparedtobulkisobserved.Thishasbeen
attributedtolargesurfacetensioninthecaseof
nanoparticles.Inordertoreleasethistension,they
meltfasterascomparedtobulk.
Encapsulationofthesenanoparticlesbysilica
greatlyimprovestheirthermalstability.
By changing the thickness of the shell, variation in
melting point is observed.
A60-70nmthickcoatingofsilicagreatlyimproves
thethermalstabilityofgoldnanoshells(about300
degreeshigher).
Coatingofsilicaonsuchshellsisawayof
preservingtheidentityofindividualcoreparticles
becauseofhightemperaturestabilityofsilica.

56. Preparation of nanoshells
Nanoshells are prepared by the following methods :
a) Surface coating of a layer of metal by physical
vapour deposition on solid substrates.
b) Thermal evaporation
c) Chemical reduction
d) Other techniques like photochemical reduction etc.

57. Nanoshellsensorsforprecisionchemicalanalysis
NanotechnologyresearchersatRiceUniversityhave
designedasensorwhichcanbespecificallyusedto
obtainchemicalinformation.Ramanspectroscopyis
themethodwidelyusedformolecularanalysis.It
involvesthestudyingofspectrumoflightthatan
objectemitstodecipherwhichelementsarepresentin
thesample.
Applications

58. Scientistshavelongknownthattheycouldboost
theRamanlightemissionsfromasamplebya
milliontimesormorejustbyplacingsmallmetal
particlescalledcolloidsnexttothesample.
Usingthesameprinciple,Rice’sresearchteamhas
developedSurfaceEnhancedRamanScattering
(SERS).Inthissensor,nanoshellsarelayered
colloidsthatconsistofacoreofnonconducting
materialcoveredbyathinmetallicshell.
Byvaryingtheshellthicknesstheelectricaland
opticalpropertiesofnanoshellscanbetuned
precisely.

59. Therapeutic and drug delivery applications
By carefully choosing a core-to-shell ratio, it is possible
to design novel nanoshell structures which either
absorb light or scatter it effectively.
Strong absorbers are used in photothermal therapy,
while efficient scatterers can be used in imaging
applications.
Core shell (mostly gold nanoshells) particles
conjugated with enzymes and antibodies can be
embedded in a matrix of a polymer.

60. ThesepolymersincludeN-isopropyl-acrylamideand
Acrylamide.Thesehaveameltingtemperature
slightlyabovebodytemperature.
Whensuchananoshellandpolymermatrixis
illuminatedwithresonantwavelength,nanoshells
absorbheatandtransfertothelocalenvironment.
Thiscausescollapseofthepolymernetworkand
hencereleaseofdrug.
Incoreshellparticlesbaseddrugdeliverysystems,
thedrugcanbeeitherencapsulatedoradsorbedon
totheshellsurface.

61. Nanoweapons to fight cancer
NanoshellsinventedatRiceUniversityhavebecomean
alternativetochemotherapybykillingONLYcancerous
cellsafterinjectionintothebloodstream.
Goldnanoshellsareusedforcancerbecausegoldis
biocompatibleandnoantibodiesareproducedagainst
it.
IRwavelengthsareusedforcancertreatmentasthey
penetratethefurthest.
Nanoshellscanbetaggedwithspecificantibodiesfor
diseasedtissuesortumours.

62. Whenthesenanoshellsareinsertedintothebody,
theygetattachedtodiseasedcellsandcanbe
imaged.
Onlocatingthetumour,itisirradiatedwith
resonancewavelengthofthespecificnanoshells
leadingtoheatingofthetumourandhence
destructionoftumourcells.
Theusualtreatmentsforcancerlikechemotherapy
orradiotherapyhavevarioussideeffectslikehair
loss,lackofappetite,diarrhoeaetc.Theprocess
ofattackingthetumouralsoleadstothelossof
thenearbyhealthycells.
Nanoshellsofferaneffectiveandrelativelysafer
strategytocurecancer.

63. Colorimetryand biosensing
Colorimetric sensing is monitoring changes in the
colour of the nanoparticles which act as sensors.
Usually gold nanoparticles are used for this purpose
and polynucleotides, oligonucleotides and DNA have
been detected successfully.
Single strand of DNA was immobilised on gold
nanoshells and was used for the detection of its
complementary DNA strand.
The intense ruby-red colour changed to blue upon
detection of the complementary DNA due to
agglomeration.

64. Immunoassay
Recently,successfuldetectionofimmunoglobulins
usinggoldnanoshellswasachievedinsaline,serum
andwholeblood.
Thissystemconstitutesasimpleimmunoassay
capableofdetectingassmallasnanogramperml
quantitiesofvariousanalytesindifferentmedia
within10minutes.
When introducedintosamplescontainingthe
appropriateantigen,theselectiveantibody-antigen
interactioncausesthegoldnanoshellstoaggregate
thusshiftingthewavelengthfurtherintotheextreme
IRregionofthespectrum.

65. Dendrimers
Dendrimersarelargeandcomplexmolecules
withverywell-definedchemicalstructures.They
arenearlyperfectmonodisperse (basically
meaning ofaconsistentsizeandform)
macromolecules witharegularandhighly
branchedthree-dimensionalarchitecture.
Dendrimersareproducedinaniterativesequence
ofreactionsteps,inwhicheachadditional
iterationleadstoahighergenerationdendrimer.
Theyconsistofthreemajorarchitectural
components:core,branches,andendgroups.

66.  Thecreationofdendrimers,using
specifically-designed chemical
reactions,isoneofthebestexamples
ofcontrolledhierarchicalsynthesis,
anapproachthatallowsthe'bottom-
up'creationofcomplexsystems.
Eachnewlayercreatesanew
'generation',withdoublethenumber
ofactivesites(calledendgroups)
and approximately double the
molecularweightoftheprevious
generation.
Oneofthemostappealingaspectsof
technologiesbasedondendrimersis
thatitisrelativelyeasytocontrol
theirsize,compositionandchemical
reactivityveryprecisely.

67. Synthesis of dendrimers
TwoMethods:DivergentandConvergent
DIVERGENT METHODS
Inthedivergentmethod,dendrimergrowsoutwardsfroma
multifunctionalcoremoleculeThecoremoleculereactswith
monomer moleculescontainingonereactiveandtwo
dormantgroupsgivingthefirstgenerationdendrimer.Then
thenewperipheryofthemoleculeisactivatedforreactions
withmoremonomers.Theprocessisrepeatedforseveral
generationsandadendrimerisbuiltlayerafterlayer.
AdvantagesandDisadvantages
Divergentapproachissuccessfulfortheproductionoflarge
quantitiesofdendrimers.Problemsoccurfromside
reactionsandincompletereactionsoftheendgroupsthat
leadtostructuredefects.Topreventsidereactionsandto
forcereactionstocompletionlargeexcessofreagentsis
required.Itcausessomedifficultiesinthepurificationof
thefinalproduct

68. CONVERGENT METHOD
Theconvergentmethodsweredevelopedasa
responsetotheweaknessesofthedivergent
synthesis.Intheconvergentapproach,the
dendrimerisconstructedstepwise,startingfrom
theendgroupsandprogressinginwards.When
thegrowingbranchedpolymericarms,called
dendrons,arelargeenough,theyareattachedto
amultifunctionalcoremolecule.
Advantages
Theconvergentgrowthmethodhasseveral
advantages.Itisrelativelyeasytopurifythe
desiredproductandtheoccurrenceofdefectsin
thefinalstructureisminimised.

70. Examples
The firstsynthesized dendrimers were
polyamidoamines (PAMAMs).Theyarealso
knownasstarburstdendrimers.Theterm
‘starburst’isatrademarkoftheDowChemicals
Company.Ammoniaisusedasthecoremolecule.
Inthepresenceofmethanolitreactswith
methylacrylateandthenethylenediamineis
added.
Attheendofeachbranchthereisafreeamino
groupthatcanreactwithtwomethylacrylate
monomersandtwoethylenediaminemolecules.

72. Properties
Size,shapeandreactivityaredeterminedbygenerationand
chemicalcompositionofthecore,interiorbranchingandsurface
functionalities.Itsdiameterincreaseslinearlypergeneration
whereasthenumberofsurfacegroupsincreasesgeometrically.
Dendrimersformatightlypackedballinsolution.Thishasagreat
impactontheirrheologicalproperties.
Dendrimersolutionshavesignificantlylowerviscositythanlinear
polymers.Whenthemolecularmassofdendrimersincreases,their
intrinsicviscositygoesthroughamaximum atthefourth
generationandthenbeginstodecline.
Thepresenceofmanychainendsisresponsibleforhighsolubility
andmiscibilityandforhighreactivity.Dendrimers’solubilityis
stronglyinfluencedbythenatureofsurfacegroups.Dendrimers
terminatedinhydrophilicgroupsaresolubleinpolarsolvents,
whiledendrimershavinghydrophobicendgroupsaresolublein
nonpolarsolvents.
Lowergenerationdendrimerswhicharelargeenoughtobe
sphericalbutdonotformatightlypackedsurface,haveenormous
surfaceareasinrelationtovolume.

73. Dendrimers havesome
uniquepropertiesbecause
oftheirglobularshape
andthepresence of
internalcavities.Themost
importantoneisthe
possibilitytoencapsulate
guestmoleculesinthe
macromoleculeinterior.

74. Advantages of dendrimers
They are synthesized as a single molecular entity
having high structural and chemical homogeneity
They offer precisely controlled macromolecular surface,
with a far lower cost than proteins.
They have broad applicability to interfere with protein-
protein interactions.
They can be used to precisely control the
pharmacokinetics of drugs.
They provide a scaffold for the attachment of multiple
functional elements in precise ratios and positions.

75. Applications
Dendrimershavebeenappliedininvitrodiagnostics.
DadeInternationalInc.(U.S.A.)hasintroducedanew
methodincardiactesting.Proteinspresentinablood
samplebindtoimmunoglobulins whicharefixedby
dendrimerstoasheetofglass.Theresultshowsifthereis
anyheartmuscledamage.
Dendrimershavebeentestedinpreclinicalstudiesas
contrastagentsformagneticresonanceTheyalsoimprove
visualisationofvascularstructuresinmagneticresonance
angiography(MRA)ofthebody
Thereareattemptstousedendrimersinthetargeted
deliveryofdrugsandothertherapeuticagents.Drug
moleculescanbeloadedbothintheinteriorofthe
dendrimersaswellasattachedtothesurfacegroups
Watersolubledendrimersarecapableofbindingand
solubilisingsmallacidichydrophobicmoleculeswith
antifungalorantibacterialproperties.Theboundsubstrates
maybereleaseduponcontactwiththetargetorganism.
Suchcomplexesmaybeconsideredaspotentialdrug
deliverysystems

76. Dendrimerscanactascarriers,calledvectorsin
genetherapy.Vectorstransfergenesthrough
thecellmembraneintothenucleus
Dendrimerscanfunctionaspumpingdevices,
concentratingreagentsinthecavityandexpelling
theproductsfromthecavity.
Dendrimersareusedinmolecularelectronicsfor
storageofinformation
Usedforseparationandmolecularrecognition
processes.
Adhesives,surfacecoatingsorpolymercross-
linking.
Scaffolds
Light-harvestingdendrimersthatcanperform
some oftheearlyfunctionsofartificial
photosynthesis.

78. SMALLER. . . smaller . . . smaller. In the
semiconductor industry, this mantra translates
to faster . . . faster . . . faster. The question is,
how small can you go?

79. Aquantumdotisasemiconductorwhoseexcitonsare
confinedinallthreespatialdimensions.Asa
result,theyhavepropertiesthatarebetween
thoseofbulksemiconductorsandthoseof
discretemolecules.
TheywerediscoveredbyLouisE.Brus,whowasthen
atBellLabsandisnowachemistryprofessorat
ColumbiaUniversity.
Theterm"QuantumDot"wascoinedbyMarkReed,
whowasthenatTexasInstrumentsandisnowa
professorofappliedphysicsatYaleUniversity.

80. Thesmallsizeresultsinnewquantumphenomena
thatyieldsomeextraordinaryproperties.
Materialpropertieschangedramaticallybecause
quantumeffectsarisefromtheconfinementof
electronsand"holes"inthematerial.
Sizechangesothermaterialpropertiessuchasthe
electricalandnonlinearopticalpropertiesofa
material,makingthemverydifferentfromthose
ofthematerial'sbulkform.
Ifadotisexcited,thesmallerthedot,thehigherthe
energyandintensityofitsemittedlight.
Hence,theseverysmall,semiconductingquantum
dotsaregatewaystoanenormousarrayof
possibleapplicationsandnewtechnologies.

81. Assmallcrystals,theycanbemixedinliquid
solutions,makingthemidealforfluorescenttagging
inbiologicalapplications.
Theyperformassecuritytaggant.
Inbeadform,theycanbeblendedintoink,making
anexcellentanti-counterfeitingpigments
Canbemadeintofilmprocessinglegendaryfor
applicationsinphotonicswitching,opticalsignal
conditioningandmodelockinglasers.
Mayserveashomelandsecuritydevices,detecting
radiationsandhelpingfightterrorism.
Applications

82. "Here at the Laboratory," says Lee, "we have made
silicon and germanium quantum dots that emit light
throughout the visible spectrum-from the infrared to
the ultraviolet. What makes our dots unique is that
their luminescence can be tuned to any wavelength
over a broad spectral range and be stable under
ambient conditions“.
Micrograph ofpyramid-shaped
quantum dots grown from
indium,gallium,andarsenic.
Eachdotisabout20nanometers
wideand8nanometers inheight.

83. Making quantum dots
•Thereareseveralwaystoconfineexcitonsinsemiconductors,
resultingindifferentmethodstoproducequantumdots.
•Ingeneral,quantumwires,wellsanddotsaregrownby
advancedepitaxialtechniquesinnanocrystalsproduced
bychemicalmethodsorbyionimplantation,orin
nanodevices made bystate-of-the-artlithographic
techniques.

84. Colloidalsynthesis
Colloidalsemiconductor nanocrystalsaresynthesizedfrom
precursorcompounds dissolvedinsolutions,muchlike
traditionalchemicalprocesses.
Thesynthesisofcolloidalquantumdotsisbasedonathree
component systemcomposed of:precursors,organic
surfactants,andsolvents.
When heatingareactionmedium toasufficientlyhigh
temperature,theprecursorschemicallytransforminto
monomers.Oncethemonomersreachahighenoughsuper
saturationlevel,thenanocrystalgrowthstartswitha
nucleationprocess.
Thetemperatureduringthegrowthprocessisoneofthecritical
factorsindeterminingoptimalconditionsforthe
nanocrystalgrowth.
Itmustbehighenoughtoallowforrearrangementandannealing
ofatomsduringthesynthesisprocesswhilebeinglow
enoughtopromotecrystalgrowth.

85. Anothercriticalfactorthathastobestringentlycontrolledduring
nanocrystalgrowthisthemonomerconcentration.
Thegrowthprocessofnanocrystalscanoccurintwodifferent
regimes,“focusing”and“defocusing”.Athighmonomer
concentrations,thecriticalsize(thesizewherenanocrystals
neithergrownorshrink)isrelativelysmall,resultingingrowth
ofnearlyallparticles.
Inthisregime,smallerparticlesgrowfasterthanlargeones(since
largercrystalsneedmoreatomstogrowthansmallcrystals)
resultingin“focusing”ofthesizedistributiontoyieldnearly
monodisperseparticles.

86. Therearecolloidalmethods toproducemany different
semiconductors,includingcadmium selenide,cadmium
sulfide,indiumarsenide,andindiumphosphide.
Thesequantumdotscancontainasfewas100to100,000atoms
withinthequantumdotvolume,withadiameterof10to50
atoms.Thiscorrespondstoabout2to10nanometers,and
at10nmindiameter,nearly3millionquantumdotscould
belinedupendtoendandfitwithinthewidthofahuman
thumb.
Largequantitiesofquantumdotsmaybesynthesizedviacolloidal
synthesis.Colloidalsynthesisisbyfarthecheapestandhas
theadvantageofbeingabletooccuratbenchtop
conditions.
Itisacknowledgedtobetheleasttoxicofallthedifferentformsof
synthesis.

87. Leeetal.(2002)reportedusinggeneticallyengineeredM13
bacteriophage virusestocreatequantum dot
biocompositestructures.
Asabackgroundtothiswork,ithadpreviouslybeenshownthat
geneticallyengineeredvirusescanrecognizespecific
semiconductorsurfacesthroughthemethodofselection
bycombinatorialphagedisplay.
Additionally,itisknownthatliquidcrystallinestructuresofwild-
typeviruses(Fd,M13,andTMV)areadjustableby
controllingthesolutionconcentrations,solutionionic
strength,andtheexternalmagneticfieldappliedtothe
solutions.
Consequently,thespecificrecognitionpropertiesoftheviruscan
beusedtoorganizeinorganicnanocrystals,forming
orderedarraysoverthelengthscaledefinedbyliquid
crystalformation.
Viral assembely

88. Usingthisinformation,Leeetal.(2000)wereabletocreateself-
assemblehighlyoriented,self-supportingfilmsfroma
phageandZnSprecursorsolution.
Thissystemallowedthemtovaryboththelengthof
bacteriophageandthetypeofinorganicmaterialthrough
geneticmodificationandselection.

89. Optical properties
Animmediateopticalfeatureofcolloidalquantumdotsistheir
coloration.Whilethematerialwhichmakesupaquantumdot
definesitsintrinsicenergysignature,thequantumconfinedsizeof
thenanocrystalismoresignificantatenergiesnearthebandgap.
Thusquantumdotsofthesamematerial,butwithdifferentsizes,
canemitlightofdifferentcolors.
Thelargerthedot,theredder(lowerenergy)its
fluorescencespectrum.Conversely,smallerdotsemitbluer(higher
energy)light.Thecolorationisdirectlyrelatedtotheenergylevels
ofthequantumdot.Quantitativelyspeaking,thebandgapenergy
thatdeterminestheenergy(andhencecolor)ofthefluorescedlight
isinverselyproportionaltothesquareofthesizeofthequantum
dot.

90. •Larger quantum dots have more energy levels which are more closely
spaced.
•This allows the quantum dot to absorb photons containing less energy,
i.e. those closer to the red end of the spectrum.
•Recent articles in nanotechnology and other journals have begun to
suggest that the shape of the quantum dot may also be a factor in the
coloration, but as yet not enough information has become available.
•Furthermore it was shown recently that the lifetime of fluorescence is
determined by the size. Larger dots have more closely spaced energy
levels in which the electron-hole pair can be trapped.
•Therefore, electron-hole pairs in larger dots live longer and thus these
large dots show a larger lifetime.
•Similar to a molecule, a quantum dot has both a quantized energy
spectrum and a quantized density of electronic states near the band edge.

91. Applications
In modern biological analysis, various kinds of organic dyes are
used.
However, with each passing year, more flexibility is being required
of these dyes, and the traditional dyes are often unable to
meet the expectations.
To this end, quantum dots have quickly filled in the role, being
found to be superior to traditional organic dyes on several
counts, one of the most immediately obvious being
brightness (owing to the high quantum yield) as well as
their stability (much less photo destruction).
Drawback:For single-particle tracking, the irregular blinking of
quantum dots is a minor drawback.
The use of quantum dots for highly sensitive cellular imaging has
seen major advances over the past decade.
Theimprovedphotostabilityofquantumdotsforexample,allows
the acquisitionofmanyconsecutivefocal-planeimages
thatcanbereconstructedintoahigh-resolutionthree-
dimensionalimage.

92. Anotherapplicationthattakesadvantageoftheextraordinary
photostabilityofquantumdotprobesisthereal-timetrackingof
moleculesandcellsoverextendedperiodsoftime.
Researcherswereabletoobservequantumdotsinlymphnodesof
miceformorethan4months.
Semiconductorquantumdotshavealsobeenemployedforinvitro
imagingofpre-labeledcells.
Theabilitytoimagesingle-cellmigrationinrealtimeisexpectedto
beimportanttoseveralresearchareassuchas
embryogenesis,cancermetastasis,stem-celltherapeutics,
andlymphocyteimmunology.
Scientistshaveproventhatquantumdotsaredramaticallybetter
thanexistingmethodsfordeliveringagene-silencingtool,
knownassiRNA,intocells.


93. •Firstattemptshavebeenmadeinusingquantumdotsfortumor
targetingunderinvivoconditions.Thereexisttwobasictargeting
schemes:activetargetingandpassivetargeting.
•Inthecaseofactivetargeting,quantumdotsarefunctionalizedwith
tumorspecificbindingsitestospecificallybindtotumorcells.
•Passivetargetingutilizesenhancedpermeationandretentionoftumor
cellsforthedeliveryofquantumdotprobes.
•Fastgrowingtumorcellstypicallyhavemorepermeablemembranes
thanhealthycells,allowingtheleakageofsmallnanoparticlesintothe
cellbody.
•Moreover,tumorcellslackaneffectivelymphaticdrainagesystem,
whichleadstosubsequentnanoparticleaccumulation.

94. •Oneoftheremainingissueswithquantumdotprobesistheirinvivo
toxicity.
•CdSenanocrystalsforexamplearehighlytoxictoculturedcells
underUVillumination.TheenergyofUVirradiationiscloseto
thecovalentchemicalbondenergyofCdSenanocrystals.
•Asaresult,semiconductorparticlescanbedissolved,inaprocess
knownasphotolysis,toreleasetoxiccadmiumionsintothe
culturemedium.
•IntheabsenceofUVirradiation,however,quantumdotswitha
stablepolymercoatinghavebeenfoundtobeessentially
nontoxic.Thenagain,onlylittleisknownabouttheexcretion
processofpolymer-protectedquantumdotsfromliving
organisms.Theseandotherquestionsmustbecarefully
examinedbeforequantumdotapplicationsintumoror
vascularimagingcanbeapprovedforhumanclinicaluse.
•Anothercuttingedgeapplicationofquantumdotsisalsobeing
researchedaspotentialinorganicfluorophoreforintra-
operativedetectionoftumorsusingfluorescencespectroscopy.

95. NANOFABRICATION

96. WHAT IS NANOFABRICATION?
Nanofabrication is the design and manufacture of
devices with dimensions measured in nanometers,
essentially dealing with dimensions less than
100nm.
Nanofabrication is of interest to computer engineers
because it opens the door to super-high-density
microprocessors and memory chips.
Nanofabrication has caught the attention of the
medical industry with regard to drug delivery
systems, nanosurgeryusing nanoroboticdevices
etc.
It is also being extensively researched for use in
military and aerospace applications.

97. Classic Approach to
fabrication:
•Top down approach–
Nanostructures are made by
stripping layer by layer from
the top. An example involves
scaling down integrated-circuit
( IC ) fabrication, i.e., by
removing one atom at a time
until the desired structure
emerges.
•Bottom up approach–This
relies on self assembly process
where nanostructures are built
atom by atom from the
bottom. An example involves
the assembly of a chip atom-
by-atom; this would resemble
bricklaying.

99. Types of nanofabrication
Nanolithography referstothefabricationof
nanometer-scale structures by patterning
substrateswithatleastonelateraldimension
betweenthesizeofanindividualatomand100nm
byemployinginteractionofbeamsofphotons.
Itresultsintheselectiveremovalordeposition
ofmaterialontoasubstrateinapredetermined
pattern.
Selfassemblyisabottomupprocessinwhich
componentsarrangethemselvesintostructured
unitsorpatternsfromabase.

100. Anyformoflithographyessentiallymeanspatterningor
printingonasmoothsurfacebyexploitingchemical
interactionstoobtainimagesorcharacters.Incaseof
nanolithography,manydifferentprinciplesareusedfor
creatingnanometerscalestructures.
The basic types:
Optical/Photolithography
Electron beam lithography
Ion beam lithography
Extreme Ultraviolet (EUV) Lithography
X-Ray Lithography
Nanolithography

101. Alternate Lithography techniques:
Micro contact printing
Nano imprint lithography
Scanned probe lithography
Dip pen lithography

102. Nanolithography (contd.)
Opticallithography
Ithasbeenthepredominantpatterntechniquesincethe
adventofthesemiconductoragewhichiscapableofproducing
some100nmpatternswiththeuseofveryshortwavelengths
(currently248-365nm).
X-Raylithography
X-raylithographycanbeextendedtoanopticalresolutionof
0.8nmbyusingtheshortwavelengthof1nanometerforthe
illumination.
Electronbeamdirectwritelithography
Theuseofabeamofelectronstoproduceapatterntypically
inapolymericresistPMMA{Polymethyl(methacrylate)}
ExtremeUltravioletlithography
Itisaformoflithographyusingultrashortwavelengths
(13.5nm).

103. Optical Lithography:
Itisaprocess used in
nanofabrication toselectively
removepartsofathinfilm(orthe
bulkofasubstrate).
Ituseslighttotransfera
geometric pattern from a
photomask toalight-sensitive
chemical(‘photoresist’,orsimply
‘resist’)onthesubstrate.
Aseriesofchemicaltreatments
thenengraves theexposure
pattern into the material
underneaththephotoresist.

104. The basic procedure involves:
Cleaning and preparation of the wafer
Exposure and developing the photoresist coated wafer
Etching/Thin film deposition/lift off
Photoresist removal
Photolithography normally employs light from sources
like gas discharge lamps with mercury and mixture of
noble gases like xenon etc. More recently deep UV
(<300nm) produced from lasers are being used.

105. Electron Beam Lithography :
It is the practice of using a beam of electrons to generate patterns
on a surface covered with a resist.
The primary advantage of electron beam lithography is that it is
one of the ways to beat the diffraction limit of light.
It uses a focused beam of electrons to form the circuit patterns
needed for material deposition on (or removal from) the wafer.
It does not use a mask, electron beams are used to directly etch on
the wafer surface.
It offers higher patterning resolution than optical lithography
because of the shorter wavelength possessed by the 10 -50 keV
electrons that it employs.

106. Ion Beam Lithography
This is a variation of the electron beam lithography technique,
using an focused ion beam (FIB) instead of an electron beam, which
scans across the substrate surface and exposes the sensitive
coating.
A grid of pixels is superimposed on the substrate surface, each
pixel having a unique address. The pattern data is transferred to the
controlling computer, which then directs the electron beam to realize
the pattern on the substrate pixel by pixel.
The advantages of ion beam lithography include
•computer controlled beam
•minimized back scattering
•no necessity for mask
•minimized diffraction effects
•higher resolution
•accurate surface feature registration
•ion sensitive resists are better responsive

107. Extreme Ultraviolet
lithography:
It uses 13.5nm EUV wavelength
All matters absorbs EUV therefore
procedure to be carried out in vacuum
All optical instruments and photo resists
are made of multilayer defect free
mirrors which reflect light by means of
interlayer interference

108. X Ray Lithography:
Theshortwavelengthsof0.8nmX-rays
overcomediffractionlimitsintheresolutionofthe
otherwisecompetentopticallithography.
DeepX-raylithographyusesyetshorter
wavelengths,about0.1nmwithmodified
procedures,tofabricatedeeperstructures

109. The mask consists of an X-ray absorber, typically of gold
or compounds of tantalum or tungsten, on a membrane
that is transparent to X-rays, typically of silicon carbide or
diamond
The figure is an example of a quantum dot array
generated by three dimensional x ray lithography:

110. Refers to a family of techniques for fabricating or replicating
structuresusing "elastomeric stamps, molds, and conformable
photomasks" It is called "soft" because it uses elastomeric
materialsmost notably PDMS(Polydimethylsiloxane). Soft
lithography is generally used to construct features measured on
the micrometer to nanometerscale.
Soft lithographyincludes the technologies of Micro Contact
Printing(µCP), Replica moulding (REM), Micro transfer
moulding (µTM), Micro moulding in capillaries (MIMIC) and
Solvent Assisted microcontact moulding (SAMIM) (From Xia et
al.) Patterning by etching at the nanoscale(PENs)
Soft Lithography

111. One of the soft lithography procedures,
Micro contact printing as discussed by Xia and Whitesides, is as
follows:
The lithographyprocedures (photolithography, EBL, etc.) are
followed to etch a desired pattern onto a substrate(usually silicon)
Next, the stamp is created by pouring a degassed resinovertop of
the etched wafer. Common resins include PDMSand Flurosilicon.
Removing the cured resin from the substrate, a stamp contoured to
your pattern is acquired.
The stamp is then "inked" by placing it in a bath of inking solution
(for example, in ethanol) and ODT (octadecanethiol) for a short
period of time(Figure 1). The ink molecules then diffuse into the
stamp (Figure 2).
The inked stamp is brought in contact with the substrate for a
certain length of time,allowing ink molecules to transfer onto the
substrate surface. The stamp is removed, leaving the desired single-
molecule thick pattern on the substrate.
Steps 4 and 5 are repeated for each substrate on which the pattern
is desired

112. Figure 2 -ODT from the solution settles
down onto the PDMSstamp. Stamp now
has ODT attached to it which acts as the
ink.
Figure1-"Inking"astamp.PDMS
stampwithpatternisplacedin
EthanolandODTsolution
Figure 3 -The PDMS stamp with
the ODT is placed on the gold
substrate. When the stamp is
removed, the ODT in contact with
the gold stays stuck to the gold.
Thus the pattern from the stamp is
transferred to the gold via the ODT
"ink."

113. Types of soft lithography
Micromoulding in capillaries (MIMIC):1um
Microtransfer moulding:250nm
Solvent Assisted Microcontact
Moulding(SAMIM):60nm
Replica Moulding
Microcontact printing:300nm

114. Isapowerfulinstrumentforimagingsurfacesattheatomiclevel.
Itsdevelopmentin1981earneditsinventors,gerdbinnigand
heinrichrohrer(at IBMzürich),thenobelprizeinphysicsin
1986.
ForanSTM,goodresolutionisconsideredtobe0.1nmlateralresolutionand
0.01nmdepthresolution.Withthisresolution,individualatoms
withinmaterialsareroutinelyimaged andmanipulated.
TheSTMcanbeusednotonlyinultrahighvacuumbutalsoinair,waterand
variousotherliquidorgasambient,andattemperaturesranging
fromnearzerokelvin'stoafewhundreddegreescelsius.
TheSTMisbasedontheconceptofquantumtunneling.Whenaconductingt
ipisbroughtveryneartothesurfacetobeexamined,abias(voltage
difference)appliedbetweenthetwocanallowelectronstotunnel
through the vacuum between them.
Scanning tunneling microscope (STM):

115. Scanning Tunneling Microscopy (STM):
In1981:DirectvisualizationofsurfaceatomswasmadeusingSTM
Tunnelingistheprocessinwhichelectronscanpassfromone
metaltoanothereventhoughtheyarenotincontact.Thisprocess
occursbycouplingofelectronicstatesbetweenthetwosurfaces
Asharptipisattachedtoapiezoelectrictranslator(materialthat
expandsandcontractsaccordingtotheamountofelectriccurrent
thattravelsthrough it)canpositionthetipwithangstrom
precision(10
-10
m)
Asthetipisscannedoverthesurface,electronsmovebetweenthe
tipandthesample.
Byattemptingtomaintainaconstantcurrentusingafeedbackloop
monitoredbyacomputerthepiezoelectricreceivesasignalfromthe
computertoraiseorlowerthetipasitscansoverthesurface.
Plottingthechangesinthetipheightandpositionproducesathree
dimensionalimagesurfaceyieldingtheabilitytoviewthelocations
ofsingleatomsandtomanipulatetheiratomicpositions.

116. Scanning tunneling microscope (STM):

117. SCANNING TUNNELING MICROSCOPE
(STM):
The resulting tunneling currentis a function of tip
position, applied voltage, and the local density of
states(LDOS) of the sample.
Information is acquired by monitoring the current as
the tip's position scans across the surface, and is
usually displayed in image form.
STM can be a challenging technique, as it can
require extremely clean and stable surfaces, sharp
tips, excellent vibration control, and sophisticated
electronics.

118. Atomic Force Microscope

120. TheAtomicForceMicroscopewasdevelopedtoovercomeabasic
drawbackwithSTM–thatitcanonlyimageconductingor
semiconductingsurfaces.TheAFMhoweverhastheadvantageof
imagingalmostanytypeofsurface,includingpolymers,ceramics,
composites,glassandbiologicalsamples.
Theatomicforcemicroscopemovesasharpprobeoverthe
specimensurfacewhilekeepingthedistancebetweentheprobetip
andthesurfaceconstant.
Itdoesthisbyexertingaverysmallamountofforceonthe
tip,justenoughtomaintainaconstantdistancebutnotenoughforce
todamagethesurface.
Theverticalmotionofthetipusuallyisfollowedbymeasuring
thedeflectionofalaserbeamthatstrikestheleverholdingthe
probe.
Unlikethescanningtunnelingmicroscope,theatomicforce
microscopecanbeusedtostudysurfacesthatdonotconduct
electricitywell. Theatomicforcemicroscopehasbeenusedto
studytheinteractionsbetweentheE.coliGroESandGroEL
chaperoninproteins,tomapplasmidsbylocatingrestrictionenzymes
boundtospecificsites,andtofollowthebehavioroflivingbacteria
andothercells.