Fabrication of low dimensional structures via template synthesis: a membrane based synthetic approach

Rajesh Kumara and S.K.Chakarvarti*

Department of Physics, Haryana College of Tech. & Mgmt., Kaithal, India

*Department of Physics, National Institute of Technology (Deemed University), Kurukshetra, India

Major objectives of my study:CONTROLLED PRODUCTION OF TRACK-ETCH MEMBRANES (TEMs)

TEMs of different diameter and shape are produced using chemical etching.

CHARACTERIZATIONS

Nanowalled microstructures of ZnS are generated through the pores of TEMs using “Template Synthesis”.

Morphological characterization using SEM

SYNTHESIS OF ZnS NANOWALLE MICROTUBULES

Fabrication of nano/micro Fabrication of nano/micro structuresstructures

Two fundamental approaches have Two fundamental approaches have been used in fabrication and been used in fabrication and processing of nano/micro structuresprocessing of nano/micro structures

Top -downTop -down

Bottom -upBottom -up

Top-down – this refers to the process of Top-down – this refers to the process of scaling down bulk structures to the nano scaling down bulk structures to the nano scale using etching and machining scale using etching and machining techniques – mechanical attrition (ball techniques – mechanical attrition (ball milling) , lithography/etchingmilling) , lithography/etching

Bottom-up – this is the building up of the Bottom-up – this is the building up of the nano structures atom by atom, or nano structures atom by atom, or molecules by molecules – powder/ Aerosol molecules by molecules – powder/ Aerosol compaction, chemical synthesis compaction, chemical synthesis (Template Synthesis)(Template Synthesis)

Template synthesis (TS)The principle of TS is producing components

through use of replication.

Nano/micro structures of controlled shape, size and very LOW dimensions are fabricated.

Easy to use and very cost effective.

Types of template methodsTypes of template methods

1. Negative template 1. Negative template synthesissynthesis

2. Positive template 2. Positive template synthesissynthesis

Negative template methodsNegative template methods Such methods use prefabricated Such methods use prefabricated

nano/micro pores or channels of pre-nano/micro pores or channels of pre-decided shape and size in solid decided shape and size in solid materials, known as templates.materials, known as templates.

The desired material is deposited The desired material is deposited into these pores by suitable into these pores by suitable methods.methods.

TEMs, AAM and mica sheets are TEMs, AAM and mica sheets are negative templates.negative templates.

Caps as overdeposited material

Fig.1.1 Schematic diagram of Template Synthesis

a) Latent tracks created by heavy ions

b) Latent tracks enlarged by chemical etching

c) Deposition of a conducting layer on one face of the membrane and electrochemical filling of the pores

d) Dissolution of the host membrane in suitable solvent, resulting in array of nano/micro structures

Heavy ions

Host insulating foil

Conducting layer

Positive template methodsPositive template methods Use wire-like structures like DNA, Use wire-like structures like DNA,

Carbon nanotubes etc as templates. Carbon nanotubes etc as templates. materials are grown on their surfaces.materials are grown on their surfaces. The physical dimensions like thickness The physical dimensions like thickness

are controlled by the amount of are controlled by the amount of material deposited.material deposited.

On removal of template, wire or tube On removal of template, wire or tube like structures are generated.like structures are generated.

Positive template methodPositive template method

ElectrodeElectrodeElectrodeElectrode DNADNA

Synthesized Synthesized StructureStructure

EXPERIMENTAL DETAILS:

NTF: Polycarbonate (Makrofol-KG)

Thickness: 10 micron

Energy: 13.6 MeV/n (U238 ions)

Flux: 106/cm2

Irradiated at GSI, Darmstadt, Germany using UNILAC facility.

* PC has high mechanical strength, * PC has high mechanical strength, toughness and is transparent.toughness and is transparent.

* Homogeneous pores can be created * Homogeneous pores can be created

* It can be easily dissolved in suitable * It can be easily dissolved in suitable solvent solvent

(a requirement for retrieval of the (a requirement for retrieval of the synthesized wires after deposition).synthesized wires after deposition).

Synthesis of nano/micro structures by ElectrodepositionSynthesis of nano/micro structures by Electrodeposition

Place membrane in aqueous

solution of metal salt

copper on bottom

M+

e-e-

M(s)M+(aq) + e-

Apply potential

Dissolve TEM

Nanoporous TEMs

Actual photograph of electrodeposition cell used in lab

Current–Time curve for the deposition Current–Time curve for the deposition of materials into TEMsof materials into TEMs

SEM photograph of ZnS SEM photograph of ZnS Nanowalled microtubulesNanowalled microtubules

0.06 M ZnCl2 + 0.05 M Na2S at 600C

Promising element for blue light emitting diodes

Protective windows and optical element

(Eg = 3.68 eV)

ZnS hollow tubulesZnS hollow tubules

# Optimum time of deposition

# Gases formation during deposition

During etching of polymer some fixed charges are formed due to

dissociation of carboxylic group on the polymer surface. Hence, TEM

become anionic in nature and electrostatic attraction contribute to absorption of material on the walls

of the pore.

Tubules formation Tubules formation mechanismmechanism

Gases evolution

t=0 t1 t2

Pore may provide an exit or out let for the gas which would push the material towards the pore wall

Template synthesis is a cost effective Template synthesis is a cost effective approach for the fabrication of approach for the fabrication of nano/micro structures and TEM act as an nano/micro structures and TEM act as an ideal template.ideal template.

Nanowalled microtubules of ZnS have Nanowalled microtubules of ZnS have been generated successfully using this been generated successfully using this technique.technique.

IMPORTANT IMPORTANT CONCLUSIONSCONCLUSIONS

THANKS THANKS FOR FOR

YOUR YOUR PATIENCE !PATIENCE !