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Pankaj B. Agarwal
Dip-Pen Nanowriting (DPN)
Pankaj Bhooshan Agarwal Sensors & Nanotechnology Group
CEERI, Pilani
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• Introduction to Nanotechnology
• Comparison of Different Nanolithography Techniques
• Atomic Force Microscopy (AFM)• Scanning Probe Lithography (SPL) Techniques
• Dip-Pen Nanolithography (DPN)
• Fundamental Kinds of DPN
• Process Steps to Work on DPN system
• Effect of Different Process Parameters on DPN
• Advance Features of DPN
• Applications of DPN• Conclusions
Outlines
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Introduction: Length Scale
Basically Nanotechnology is multi-disciplinary.
Nanoscale Devices:
Electronic devices that are designed with
lateral features of 100 nm or less.
Nanoelectronics includes nanoscalecircuits and devices including ultra-scaled
FETs, SETs, RTDs, spin devices,molecular electronic devices, and carbonnanotube
based FETs
etc.
Introduction to Nanotechnology
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There are three key factors limitingcontinued scaling in CMOS:
1.
Minimum dimensions that canbe fabricated
2.
Diminishing returns in switching
performance3.
Off-state leakage
The number of transistors
per square inch on integrated circuits
had doubledevery year. Moore predicted
that this trend would continue for the foreseeablefuture.In subsequent years, the pace slowed down a bit, but data density has doubledapproximately every 18 months, and this is the current definition of Moore's Law.
Moore’s Law
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Limitations of Optical Lithography
Minimum feature size = kλ/NAWhere
k = proportionality factor (typically 0.5 for diffraction limited systems)λ = wavelengthNA = numerical aperture = sin α(2α = acceptance angle of lens at point of focus)
• measure of light gathering power of lens
However, depth of focus = λ/(NA)2
(important because wafers are not flat)
Increasing NA is not the answer.
Reduce λ to reduce feature size.
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* Single material at a time
Comparison of Different Nanolithography Techniques
Serial/
ParallelMaterial
FlexibilityResolution Accuracy Speed
EquipmentCost
Photo-
lithography
Parallel No 100 nm High Very Fast $10M++
E-BeamLithography
Serial No 15 nm High Slow $1M-$20M
Micro-contact
Printing
Parallel Yes* 150 nm Low Fast $600k
Nanoimprint
Lithography
Parallel No 20 nm Low Fast $700k
DPN Serial/
ParallelYES 15 nm High High With
ParallelPens
$300k
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Atomic Force Microscopy (AFM)
AFM is based on themeasurement of thedifferent forces (likeattraction, repulsion,Vander Wall’s) between asharp tip & sample
surface. The nature of theforce depends upon thedistance between the tipand sample surface.
AFM is capable of investigating surfaces of both
conductor & insulator.Courtesy: G. Binnig, C. F. Quate and Ch. Gerber, PRL 56, 930 (1986)
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Schematic View of AFM System
AFM: Schematic Principle
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In Scanning Probe Lithography (SPL) technique, the AFM/STM tip is used to change the surface
chemistry of nano-dimensional area selectively.
Types of SPL with different writing mechanisms:
• Bias-induced Nanolithography,• Dip-Pen Nanolithography (DPN),
• Catalytic-probe Lithography, and• Nanografting
Scanning Probe Lithography (SPL) Techniques
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In bias-induced nanolithography, patterns
are traced with a metal-coated tip at
elevated bias onto a conductive or
semiconductive substrate.
In DPN, patterns are written with a tip
coated with ink by liquid transfer through
a capillary meniscus onto bare surfaces
to form SAMs.
In catalytic-probe lithography, a catalytic
reaction occurs where a coated tip
touches the surface to chemically change
the head groups of SAMs.
For nano-grafting, SAM molecules
assemble on a gold surface from solutiononto areas shaved by force with a
scanning atomic force microscope tip.
Various Scanning Probe Lithography (SPL) methods for SAMs
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DPN was introduced by Mirkin
Group to the research community forfabricating the nanostructures in year 1999. In this technique, ink on asharp object is transported to a paper substrate via capillary forces.
Schematic representation of DPN. A water meniscus forms
between the AFM tip coated with ODT and the Au substrate.
Quill Pen DPN
Dip-Pen Nanolithography (DPN)
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In particular, n-alkanethiol molecules (and their derivatives) are suspended indroplets at the end of an AFM tip as a molecular ink. By rastering the probe tipclose to a gold (or other metal) surface, the alkanethiol molecules aretransported to the surface via capillary action through a water meniscus thatnaturally occurs between the tip and sample in ambient conditions. An array of
molecules are deposited that is a direct function of the rastering pattern of the AFM tip.
Basic Concept of DPN
Image shows a moving AFM head depositing "ink" molecules on thesubstrate through the water meniscus.
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When molecule-substrate interactions is the spontaneous self organization ofatoms and molecules on surfaces into well-ordered arrays, called as Self- Assembled Monolayer.
Self-Assembled Monolayers (SAMs)
•
A thiol is a sulphur-containing organiccompound with the general formula RSHwhere R is arbitrary. An example is ethylmercaptan,C2
H5
SH.
•
CH3
(CH2
)H3
(CH2
)n
SH, Where n=1, 3, 5, 7,9, 11, 15, 17, 21; can form closely packedstable SAMs on gold.
•
It is believed that the terminal H atom isremoved and S forms a covalent bond withthe gold surface.
Alkanethiol SAM on Gold Substrate
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Self-Assembled Monolayers (SAMs)
Self-Assembled Monolayer of Alkanethiol on Gold
Why alkyl chains aretilted during assembling?
There is strong VanderWalls interaction between
the alkyl chains thatcauses the axis of thealkyl chains to tilt by 300
from the surface normal.
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Direct Write: –
Write the molecule ofinterest directly onto thesurface as the ink.
Templating: –
Write out an ink pattern in order to create,or attach something else.
Two Fundamental Kinds of DPN Methods
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Charge-based Recognition
Specific Binding of Ligands
DPN Templates: Molecular Glue
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Prepare Environmental Conditions
Design Pattern in InkCAD
Inking (Check whether ink isdiffusing on the Substrate)
Writing Designed Pattern &
Imaging
Ink Calibration
Process Steps to Work on DPN System
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Prepare Environmental Conditions
Process Steps to Work on DPN System
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Humidity Range:Minimum: 5% Rh,
Maximum: 75% Rh (below dew point)
Temperature Range:Minimum: 2°C less than RTMaximum: up to 10°C greater than RT
Prepare Environmental Conditions
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Prepare Environmental Conditions
Design Pattern in InkCAD
Process Steps to Work on DPN System
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InkCAD Window
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InkCAD Window
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Prepare Environmental Conditions
Design Pattern in InkCAD
Inking (Check whether ink is
diffusing on the Substrate)
Process Steps to Work on DPN System
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Coating of Tips & Inking Testing
P St t W k DPN S t
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Prepare Environmental Conditions
Design Pattern in InkCAD
Inking (Check whether ink is
diffusing on the Substrate)
Ink Calibration
Process Steps to Work on DPN System
I k C lib ti (MHA G ld S b t t )
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Calculated Line Diffusion Coefficient: 0.018 µm2/sec
Line Width: 60 nm
Ink Calibration (MHA on Gold Substrate)
P St t W k DPN S t
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Prepare Environmental Conditions
Design Pattern in InkCAD
Inking (Check whether ink is
diffusing on the Substrate)
Ink Calibration
Writing Designed Pattern &
Imaging
Process Steps to Work on DPN System
W iti D i d P tt
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Writing Designed Pattern
Effect of Different Parameters on DPN Process
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There are various parameters, which controls the writing phenomena orwe can say which decides the dot size / line width are as follows:
Substrate-Ink Combination
Substrate Roughness
Dwell Time/Speed
Humidity
Temperature
Tip Radius
Effect of Different Parameters on DPN Process
Substrate Ink Combination
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Ink Substrate Notes
Alkylthiols (e.g. ODT
and MHA)
Au 30 nm resolution with sharp tips on single crystal surfaces,
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Hydrogen
Carbon
Sulphur
Oxygen
MHA (C16
H32
O2
S)
ODT (C H S)
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ODT (C18
H38
S)
Hydrogen
Carbon
Sulphur
Substrate Roughness
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LFM images of MHA lines written on: (a) mica-peeled gold, yielding 14nm
minimum line width (b) evaporated gold, yielding 26nm minimum line width and
(c) sputtered gold, yielding 69nm minimum line width.
Substrate Roughness
Courtesy: J. haaheim et. al., Ultramicroscopy 103, 117 (2005)
Dwell Time/Speed
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(a) Shows LFM images of ODT islands deposited on a gold surface by an
ODT-coated AFM tip for sequentially longer tip-surface contact and (b) Themeasured island radii as a function of contact time. The solid line is a fit to
the radial diffusion model described in the text. The dashed line is a fit to
an alternate model requiring t1/2
dependence.
Dwell Time/Speed
Humidity Effects
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Normalized radii (with respect to maximum radius) of MHA islands
as a
function of deposition time and relative humidity.
Note: ODT shows a little dependency of the writing speed on the
ambient humidity.
Humidity Effects
Solubility of ink in water decides the ink diffusion process.
Temperature Effects
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Temperature Effects
The temperature dependencies of the growth rate of (A) ODT and (B) MHA
SAMs constructed from LFM images of dots, which were generated at nine
different temperatures in the 22-33°C temperature range (Dwell Times: 2, 4,
and 8 Seconds)
The total number of solvated molecules taking part in the transport
process increases with increasing temperature because the ink
dissolution/ desorption
process, which involves breaking and making
of van der
Waals
interactions, is facilitated.
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Advance Features of DPN System
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•
Multiple Pens
•
Bias Option (Nano-Oxidation)•
Universal Inkwells
•
2D-Nano Print Array
Advance Features of DPN System
Types of Pens
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Pens
Passive Active
Single Pens Multiple Pens (Parallel Pens)
Types of Pens
Passive Pens
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ass e e s
Active Pens
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Those are similar the multiple pen array only difference is that even
you can select/actuate particular pen at a time.
HOW ?
Nano-Oxidation:
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Basic Concept:
In this process the bias is appliedbetween tip and substrate. The
water molecules (within themeniscus) between tip andsurface are ionized and reactswith surface to make its oxide
form. Applications:
Useful to oxidize the metallic and
semiconductor surface at nano-
level.
In above experiment the 11 mm silicon oxide line is fabricated on silicon surface by
applying a sequence of 23X104
pulses of 20 V for 1 ms. The achieved oxide line width is ~13 nm.
Courtesy: M. Calleja et. al., APL 76, 3427 (2000)
Nano-Oxidation process carried out
at Silicon Substrate (CEERI Sample)
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Control bias: 5 volts
Measured Line Width ~ 100 nm* Biasing control is for passive pens only.
In Nscriptor DPN System thereis bias control option, in whichupto 200 volts can be applied
between tip and substrate.
at Silicon Substrate (CEERI Sample)
Universal
Inkwells
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Inkwells
2D Nano-Print array
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Applications for DPN
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• Biomolecular Micro-
and Nanoarrays
•
Controlling Biorecognition Processes from
the Molecular to Cellular Level
• DPN Templates
• DPN Patterned Etch Resist
Major Applications of DPN
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Fabrication of NIL Master Stamp
Applications
Cancer Diagnosis
Fabrication ofTunnel Junction
Nano-electronic
DevicesFabrication
HIV detection
DNA Writing
MHA/ODT as Etch Resist for Nano-patterning:
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1.
“Write” regions ofoctadecanethiol (ODT)
on Au thin film.
2.
Selectively etch Au using
wet chemical etchant(ferri/ferrocyanide 8-10 min).
3. Remove Ti and SiO2
, etchSi, and passivate Sisurface.
10 nm Au5 nm TiNative SiO2
Si (100)
Si(111) Si(100)
Si (100)
Weinberger et al Adv. Mater. 12, 1600 (2000).
Fabrication of Single Electron Devices:
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Silicon Nanoparticle synthesis
Electrode Structure formationMHAMHA
Gold Substrate
10-40 nm
Fabrication of NIL Master Stamp
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10 nm Au5 nm TiNative SiO2
Si (100)
Si(111) Si(100)
Si (100)
Si(111) Si(100)
NIL Master Stamp
Si
Line Test Pattern
(NIL M t St F b i t d i DPN)
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(NIL Master Stamp were Fabricated using DPN)
Cancer Diagnosis
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The tumor markers are used for detection and diagnosis ofcancer.
What are the Tumor Markers ?
• Found in the blood, other body fluids, or tissues•
High level of tumor marker may mean that a certain type ofcancer is in the body.
• Examples of tumor markers includeCA 125 (ovarian cancer),CA 15-3 (breast cancer),CEA (ovarian, lung, breast, pancreas, and gastrointestinaltract cancers), andPSA (prostate cancer).
Cancer Diagnosis
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SAM Layer Patterning Immobilization of monoclonalantibodies
Tumor markers interacts with
monoclonal antibodiesSurface Profile Detection
Direct-Write DNA Patterns on Gold Substrate
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AFM image of hexanethiol-modified oligonucleotides patterned on
polycrystalline gold.
Unmodified silicon nitride cantilevers often yield DNA patternswith feature sizes and shapes that are not easily controlled.
Then how direct writing is possible?
Improved control over DNA patterning can beachieved through surface modification of asilicon nitride AFM cantilever with 39-amino-
propyl-trimethoxysilane, which promotesreliable adhesion of the DNA ink to the tipsurface.
DNA ink:Hexanethiol-modified oligonucleotides
Courtesy: L. M. Demers et. al., Science 296, 1836 (2002)
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Schematic representation of the Nano-Immunoassay Formation
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Pankaj B. AgarwalCourtesy: Nanoink Inc.
Why DPN generated template is better option ini t th il bl t h i ?
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comparison to other available techniques?
•
We can detect at much lowerconcentrations of HIV relative to currentscreens (Enzyme-linked immunosorbent
i.e., ELISA).
•
We detect HIV in patient plasma with amuch lower number of viral copy countsthan PCR (Polymerase chain reaction.)
DPN h d t th lith l h t h i
Conclusions
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DPN has many advantages over other nanolitholgraphy techniques
e.g. High resolution (minimum line width reported: 14 nm) Material flexibility Fast writing process with parallel pens
Low Cost Process
Extensive chemistry is involved in DPN: So there is a lot of scope forchemistry researchers.
Both direct writing and templating are possible.
In the era of inter-disciplinary, it makes bridge among different areas
of science like chemistry, biology, physics, material science.
DPN has enormous applications, which are not limited to only singlearea but in various fields e.g. electronics, nanobiotechnology, biosensors
etc.
Nscriptor DPN System in CEERI:
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