DPN Presentation

8/9/2019 DPN Presentation

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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



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.



* 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



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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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



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InkCAD Window


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InkCAD Window


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Inking (Check whether ink is

diffusing on the Substrate)



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Coating of Tips & Inking Testing

P St t W k DPN S t


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Ink Calibration


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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Ink Calibration

Writing Designed Pattern &

Imaging


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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Documents

DPN Presentation