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Optical nanoantennas

Studenti:

Federico Zavanella

Betis Zeneli

Antonella Zito

Bio micro and nano systems

POLITECNICO DI TORINO

CORSO DI LAURA MAGISTRALE IN INGEGNERIA BIOMEDICA

Overview

INTRODUCTION

WORKING PRINCIPLES

FABRICATION METHODS:

Electron-beam lithography

Focused ion-beam milling

Nanoimprint lithography

GEOMETRIES

APPLICATIONS:

Biological and biomedical applications

Exemplifying application for tumor ablation

Self and AFM based assembly

SIMULATIONS:

Coventor

Comsol

Results

CONCLUSIONS AND COMMENTS

Working Principle

Traditoinal antennas can

EXCHANGE ENERGY WITH

ITS SURROUNDINGS as well

as information by means of EM

fields

Shrinking dimensions to NANOSCALE allows enhenced

interaction between IR or visible light and nanoscale matter,

enabling several kind of applications

Working Principle

LOCALIZED SURFACE PLASMON RESONANCE

For certain

materials, such as

gold and silver, it

happens to appear

close to the visible

spectral range

Thanks to LSPR we

can consider

plasmonic

nanostructures as

nanoantennas

Fabrication Methods

The resonance of optical antennas strongly depends on the

exact geometry and dimensions. In order to obtain high-

definition nanostructures (required <10nm), a combination of

both TOP-DOWN and BOTTOM-UP approaches can be used.

Some of the most popular techniques to fabricate nano

antennas:

Electron-beam lithography (EBL)

Focused ion-beam milling (FIB)

Nanoimprint lithography (NIL)

Self and AFM based assembly

Fabrication Methods

Direct patterning by a focused beam

on flat surfaces covered with an

electron sensitive material (i.e.

PMMA)

Resolutions below 5nm

Adhesion layer required

Low throughput and high costs

ELECTRON-BEAM LITHOGRAPHY

Fabrication Methods

Localized sputtering of conductive

material (by means of a focused Ga

ion beam) for a direct pattern

Resolution: 10-15 nm

Sputtered material contamination

and ion implantation issues

FOCUSED ION-BEAM MILLING

Fabrication Methods

Pattern created by

mechanically deformed

resist layer

Resolution:

10 up to 5 nm

Variations:

UV nanoimprinting

lithography and soft

nanoimprinting

techniques

NANOIMPRINTING LITHOGRAPHY

High throughput and low cost, suitable for large areas

Fabrication Methods

Chemically grown

nanostructures: controlled

shape, purity and

cristallinity

Pattern obtained by

(AFM)nanomanipulation,

electrophoresis, fluidic

alignment or micro-

contact printing

SELF AND AFM BASED ASSEMBLY

Less perfect than lithographed strucures, but narrow (1nm) gaps can be achieved, depending on the surfactant layer used

High throughput

Geometries

Since the aim is to exploit plasmon resonance effects, size,

shape and surface properties must be well defined

The geometry strongly influence antennas’ characteristics

Several designs are being analyzed in order to optimize its

characteristics

Geometries

A much intense near field can be obteined by coupling these

elementary shapes into nanospheres and nanorods DIMERS.

In the most simple case, a SINGLE METAL NANOSPHERE

can constitute a nanoantenna

An elongated particles (NANORODS) may enhance the e.f.

near its ends.

Geometries

Losses issues related to the volume.

BOW-TIE nanoantennas possess

broad band width and high field

enhancement in the gap

the radius of curvature at the apex

strongly influences its behavior

YAGI-UDA structures, whose

parameters are designed as in their

RF counterparts

Geometries

Better field localization

CROSS nanoantennas consist of two

perpendicular dipole sharing a common

gap

The two field components coherently add

up in the gap region

Applications

Lots of possible applications can take advantage of optical

antennas properties:

Optical DETECTORS

SOLAR CELLS

…

BIOLOGICAL and BIOMEDICAL applications NEXT>

Applications

Applications

LSPR depends on the

dielectric constant of the

surrounding medium

Varying Ɛm, the SPR

wavelength changes

Nanoparticles can be

detected as an Ɛm

variation

Thanks to their high

value shape factor, gold

NANORODS are suited

for this application

BIOSENSING

Applications

Nanoantennas could be exploited as imaging probes or contrast agents due to their optical, elecrtronic, magnetic and structural properties

MRI, MSR, PET and SPECT could be enhanced, as well as fluorescent emission and Raman spectroscopy

An example shows targeted molecules within the cell enviroment:

BIOMOLECULES IMAGING

Applications

An example: array of gold

nanoantennas laced into

an artificial membrane

enhances the fluorescence

intensity of three different

molecules (blue, green

and red flashes)

This minimally invasive

technique allows to

observe molecule’s

movements and

interaction within the

cellular environment

BIOMOLECULES IMAGING

Applications

Nanoparticles like nanosphere, nanorods and nanoshells can

improve the SPECIFICITY of traditional cancer ablation

practices:

PHOTO-THERMAL THERAPY

Tumors can be TARGETED by a remote control process

NIR light is absorbed by the antennas

SPR allows efficient photo-thermal conversion to HEAT

Exemplifying Application

Gold nanorods

coated with

PEG for

biocompatibility

and drug

release

Tumors were induced in mice

and PEG-NRs injected into them

PEG-NRs behavior was analized during the study

Photo thermal theraphy was delivered

Nanoshalls and Nanorods was compared, then the latters were

optimazed for near IR plasmon resonance


Irradiation regimens was arranged by investigating the ability of

PEG-NRs to act as X-ray absorbing agents (X-ray contrast ∝ NR

concentration)

RESULTS depends on:

Material characteristics and external parameters

Shape of nanoparticles, which gives absorption efficacy and

circulation times (for nanoparticle accumulation in tumor)

Irradiation protocol and nanoantenna dosing regimen


Quantitative bio-

distribution data,

incorporated into

COMPUTATIONAL

MODELING could

provide a priori

personalization of

irradiation regimens,

thanks to a rapid photo

thermal temperature

gradients calculation.


Simulations

In COVENTOR

In COMSOL 4.3

Simulations

BOW-TIE NANOANTENNA MODEL in COVENTOR:

Simulations

BOW-TIE NANOANTENNA MODEL in COVENTOR:

Start from a 100 nm of silica substrate as bottom layer

Phisical vapour deposition of a 70 nm layer of ITO

90 nm PMMA resist layer by spin casting and soft baking

PRODUCTION STEPS:

EBL patterning

Resist development in MIBK:IPA for 70’’ and rinse with IPA

PVD of 50 nm golden film

Lift off in ultrasonic acetone bath for approx. 3’

Simulations

antenna designed in terms of gap

size, flare angle, height of the arms

supposed to be done in perfect

electric conductor on FR4 substrate

BOW-TIE NANOANTENNA MODEL in COMSOL:

Analysis conducted thanks to the

radio-frequency and heat transfer

modules provided infos about :

Behavior of EM waves

Bioheat transfer in human tissues

Simulations

A sphere of uman tissue around the

anntenna were considered, phisical

properties of human liver follows:

Electrical cond. σ 0.333 S/m

Thermal cond. k 0.512 W/(m*K)

Density ρ 1060 kg/m³

Heat cap. Cp 3600 J/(kg*K)

Rel. Permitt. 1

Rel. Permeab. μ 1


Simulations

Exitation frequency 250-350 GHz

Gap size 1-10 μm

Flare angle 30-90°

Antenna height 100-500 μm

Time of exposure 60 s

The blood flow effects

have been considerated

throw the following

parameters:

Blood Temp. 37°C

B. Specific Heat 4180 J/(kg*K)

B. Perfusion rate 6.4*10

B. Density 1000kg/m³

So the best values for

antenna’s parameters

were figured out starting

from these ranges:


Results

THERMAL BEHAVIOR of the system (HEATING exploited as

tumor ablation technique requires T > 45°C/50°C)

EMISSION PATTERNS

Results

TEMPERATURE Vs TIME

Results

0.01 s 1 s 30 s

TEMPERATURE Vs TIME

ISOTHERMAL SURFACE: 50°C

Results

TEMPERATURE as a function of FREQUENCY

f 0

Results


T Vs fo

Results


Results

TEMPERATURE as a function of GAP

Gap size

Results

TEMPERATURE as a function of GAP

T Vs Gap size

Results


Results

TEMPERATURE as a function of the ARM LENGTH

T Vs arm length

Results

TEMPERATURE as a function of the FLARE ANGLE

T Vs θ

θ

Results

EMISSION PATTERNS

Electric field Vs fo

Results

EMISSION PATTERNS

Electric field Vs gap size

Results

EMISSION PATTERNS

Electric field Vs

arm length

Results

EMISSION PATTERNS

Electric field Vs

flare angle

Results

EMISSION PATTERNS

Results

OPTIMIZATION OF THE VARIABLES

fo 300 GHz

Gap 5 μm

θ 70°

ho 350 μm

TEMPERATURE Vs TIME

Results


Isosurface at 50°C Temperature distribution

- THERMAL BEHAVIOR -

Results


- EMISSION PATTERN -

Electric field

Conclusion and comments

At 200 GHz

resonation

occurs, for a

λ = 1.5 mm

(comparable with

device’s length)

Conclusion and comments

A 300 GHz wave successfully induces an electric field strongly

localized in the gap, which in turn produce heat, warming up

the tissue above 50° C

A temperature above 50°C is enough to cause cells

apoptosis, especially in tumors, due to their disorganized

vascular system

A compromise was necessary to be found for the frequency

value, taking into consideration required heating and

interaction with tissues

Thankyou for the attention

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