International Workshop On Plasma Diagnostics And Applications (iwpda_2009)

International Workshop on Plasma Diagnostics and Applications (IWPDA_2009) July 2-3, 2009, Singapore

Nanoparticles and Nanostructures fabrication through plasma route M.P. Srivastava Department of Physics and Astrophysics, University of Delhi, Delhi- 110007, INDIA

What is Nano ? 1 nanometer = 10-9 meter Some Examples that occur in nature  Consider one Hydrogen atom

 Radius of Nucleus ~ 10-6 nm  Bohr Radius ~ 0.05 nm

DNA (width) ~ 2 nm

Polio Virus ~ 100 nm

Nanoparticles  Ultra fine particles whose size is of the order of nanometer.  Effectively a bridge between bulk materials and atomic or molecular structures. Nanoparticles have very high surface area to volume ratio as compared to bulk

Nanostructures  Any solid object with at least one of its dimension within the nanometer to the tens of nanometer range

Nanoassembly ■ Includes irregular shape fractals, clusters and macromolecules that are larger than 1 nm in size. ■ It also incorporates associations of individual nanostructures and elementary nanoassemblies

What is Quantum Dot ?

Carbon Nanotubes (CNT’s) 

There are two types of CNT: -- single-walled (SWNT) -- one tube -- multi-walled (MWNT) -- several concentric tubes TUBE 1 TUBE 2 TUBE 3

(SWNT) (MWNT)



Produced mainly by 3 techniques : -- Arc-discharge (cheaper method) -- laser-ablation

-- catalytic growth

Change in different properties at nanoscale:

Surface Properties Nanoscale gold particles can be orange, purple, red, or greenish, depending on their size

Optical Properties Reflection, Absorption and Transmission co-efficient, Refractive Index changes at Nanoscale Change is due to nature of interaction among the atoms and that between atoms and electromagnetic waves

energy

σ* p

Conduction band

sp3

Electronic Properties

energy gap

σ s atom

molecule Quantum dot

Valence band

No. of connected atoms

Electronic energy levels depend on the number of binding atoms. By binding more and more atoms together, the discrete energy levels of the atomic

orbitals merge into energy bands (here shown for a semiconducting material).

Change in Electronic Property  Due to increase in band gap, if the bulk material is

conducting then it will become semi-conducting and if the bulk material is semi-conducting, it will become insulating

Change in Optical Property Light with energy lower than Eg cannot be absorbed by the quantum dot, so its absorption spectrum shifts towards blue (shorter wavelength) w. r. t. the bulk material Eg = hc / λ As Eg increases, λ decreases

Thermal Properties Because of the change in the random motion of the atoms due to atomic interaction there is change in melting point and specific heat

Magnetic Properties Due to change in the magnetic dipole moments there is change in magnetic susceptibility and non-magnetic material can become magnetic and vice-versa.

How do we See different sized objects ?

objects

T

TRNASMISSION ELECTRON MICROSCOPY  Is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as they pass through.  Objects of the order of a few angstrom (10-10 m) can be seen.  Works by passing electrons through the sample and using magnetic lenses to focus the image of the structure The samples must be very thin (usually less than 100 nm), so that many electrons can be transmitted across the specimen.

Scanning Electron Microscope  SEM is an instrument that produces a largely magnified image by using electrons instead of light to form an image.  Beam of electrons is produced at the top of the microscope by an electron gun. Electron beam follows a vertical path through the microscope, which is held within a vacuum. Beam travels through electromagnetic fields and lenses, which focus the beam down toward the sample.

 Once the beam hits the sample, electrons and X-rays are ejected from the sample.

Scanning probe microscopy (SPM)

 SPM provides surface structural (3- dimensional real-space images of nanostructures) and electronic information with atomic resolution  SPM uses the interaction between a sharp conducting tip and a sample surface to obtain an image. The sharp tip is held very close to the surface to be examined and is scanned back-and-forth A topographic image of the surface can be obtained by making measurements at different locations, by scanning the probe at constant height

Under the category of SPM we will discuss briefly Scanning Tunneling Microscope (STM) Atomic Force Microscope (AFM) Magnetic Force Microscope (MFM)

Scanning Tunneling Microscope (STM) ♦ The interaction between the probe tip (metallic) and the sample surface is electrical which causes electron tunneling. ♦ This technique measures the tunneling current flowing between the probe tip and the sample, as they are held a small distance apart and an electric field is applied between them.

Atomic Force Microscopy  AFM can image insulating materials as it is based on atomic force between the tip and the surface

Depending on the separation between the tip and the sample, various forces play the dominant role : If tip is extremely close to the surface, short – range repulsive part of the van der Waals forces play the dominant role When the tip is lifted above the surface, long – range attractive interactions play an important role

TWO approaches of nanofabrication

 Top-down Are good for producing structures with long-range order and for making macroscopic connections

 Bottom-up Are best suited for assembly and establishing shortrange order at nanoscale dimensions.

Top Down 

It involves taking a large chunk of material and

slicing

up into many wafers.

Bulk material

Sliced Bulk material

it

Further slicing

Slicing till nanoscale

Bottom Up 

Instead of whittling down a big block of material, we build from

the ground up: creating molecules on a surface and then allowing them to assemble into larger structures by adding atom by atom.

 Bottom-up, or self-assembly, approaches to nanofabrication use chemical or physical forces operating at the nanoscale to assemble basic units into larger structures.  Bottom-up approaches comes from biological systems, where nature has harnessed chemical forces to create essentially all the structures needed by life.  In laboratory this approach is achieved by plasma methods or by ionized beam techniques.

Types of PLASMA o Low

temperature  Temperature ~ fractions to a few tens of eV  Low degree of ionization

o High

temperature  Temperature ~ few KeV or even more  Plasma is in fully ionized state  common in nuclear fusion devices or stellar interiors

Low temperature and High temperature plasma are classified in two parts: Thermal equilibrium  Te~Ti~Tn ~1 eV~ 11600K  Neutral gas environment is hot enough to melt and evaporate solid material

 Degree of ionization is substantial

Non- Thermal equilibrium  Te>> Ti and Tn; Te~1-2 eV and Ti~Tn~0,026 eV  Such plasmas are created in gas discharges when an ac or dc electric current passes through neutral gas or when gas is subjected to rf, or microwave.  Degree of ionization ~ 10-5-10-2

♣ further class of low temperature discharge occurs in gases at

atmospheric pressure ♣ this class is out of thermal equilibrium ♣ includes corona, spark, dielectric barrier etc.. ♣ collision rate is high ♣ discharge doesn’t not reach thermal equilibrium as it is short lived ☼ Pulsed laboratory plasma systems could be hot plasma but are out of thermal equilibrium as they are short lived

Different Plasma Fabrication techniques of Nanoparticles and Nanostructures

DC Glow Discharge globally neutral, but contains regions of net positive and negative charge ☼

☼ electron and ion density ~ 108 – 1014 m-3 ☼ number of neutral atoms or molecules ~ 1020 m-3 ☼ Degree of ionization ~ 10 -4

Arc-discharge  Characterized by the high energy content and the local thermal equilibrium state (LTE) ANODE PLASMA CATHODE

 Two electrodes are used to produce a dc =

electric arc-discharge in inert gas atmosphere  Classified as : Thermal arc and Vapor arc

Micro tubes of graphitic carbon by thermal arc-discharge Ijima [ Nature 354, 1991, 7]

RF Sputtering

SEM images of ZnO nanobelts by RF Sputtering at magnification of (a) 10,000 and (b) 25,000. Supab Choopuna, Niyom Hongsitha, Sornchai Tanunchaia, Torranin Chairuangsrib, Chatchai Krua-ina, Somsorn Singkarata,Thirapat Vilaithonga, Pongsri Mangkorntonga, Nikorn Mangkorntonga [Journal of Crystal Growth 282 (2005) 365–369]

Pulsed laser deposition (PLD) Is a technique where a high powered pulsed laser beam is focused inside a vacuum chamber to strike a target of the desired composition. Material is then vaporized from the target and deposited as a thin film on a substrate, such as a silicon wafer facing the target.

nanostructures grown using PLD technique

A

SEM images of ZnO nanowires J Zúñiga-Pérez, A Rahm, C Czekalla, J Lenzner, M Lorenz and M Grundmann [Nanotechnology 18 (2007) 195303]

B SEM images of indium–tin oxide nanostructures deposited at 0.1 mbar (a, b), 0.5 mbar (c, d), 1 mbar (e, f) and 2 mbar (g, h)

Raluca Savu and Ednan Joanni [Scripta Materialia 55 (2006) 979–981]

Electron cyclotron resonance magnetron sputtering (ECR-MS)

 Microwave frequencies ~2.45 GHz,

with a strong magnetic field B,  Plasma densities (1017− 1018 m−3) Working pressures (0.1–10 mTorr) The ion energy can be controlled by additional substrate bias.

SEM images of CNx films deposited on 440C stainless steel with ECR assisted dc magnetron sputtering Ming Y. Chen, Daniel J. Kramer [Thin Solid Films 382, 2001, 4]

Different types of Nanostructures grown using some other plasma routes

Plasma-assisted cathodic arc deposition

SEM plan views acquired from the ZrO2 thin films prepared at substrate temperature of 823 K soaked in simulated body fluids (SBF) solution for 14 days Weifeng Li, Xuanyong Liu, Anping Huang and Paul K Chu [J. Phys. D: Appl. Phys. 40 (2007) 2293–2299]

Low pressure silane plasmas

cubic-shaped silicon nanocrystals Ameya Bapat, Marco Gatti, Yong-Ping Ding, Stephen A Campbell and Uwe Kortshagen [J. Phys. D: Appl. Phys. 40 (2007) 2247–2257]

Plasma produced in Postglow reactor

SEM images of (a) Pure niobium foil , (b) the thermally oxidized niobium foil and (c) the Nb2O5 nanowires covered niobium foil U Cvelbar and M Mozetiˇc [J. Phys. D: Appl. Phys. 40 (2007) 2300–2303]

RF induction plasma

FE-SEM images of TiO2 nanoparticles synthesized with 100 L min−1 of counter-flow He as the quench gas J-G Li, M Ikeda, R Ye, Y Moriyoshi and T Ishigaki [J. Phys. D: Appl. Phys. 40 (2007) 2348–2353]

Nanofabrication by plasma under fusion conditions such as present in Dense Plasma Focus Device

Earlier, it was generally believed that the ions produced in high temperature, high density and strongly non-equilibrium plasma such as prevailing under fusion conditions are not useful for material

processing. It has been established in a series of papers that ions produced from hot dense plasma similar to fusion conditions such as the one

prevailing in Dense Plasma Focus (DPF) can be used for preparation of nanoparticles and nanostructures

DENSE PLASMA FOCUS (DPF) DEVICE at University of Delhi 3.3 KJ Mather type device

Source of hot dense plasma (densities of the order of 1025-1026 m-3, temperature of the order of 1-2 KeV

Dense Plasma Focus device with its modifications PRESSURE GAUGE ARGON GAS INLET

TO ROTARY PUMP MOVABLE BRASS MOUNT

SUBSTRATE HOLDER SHUTTER GLASS WINDOW CATHODE ANODE GLASS INSULATOR

FOCUS CHAMBER

-

ISOLATING CAPACITOR SPARK GAP

T.V. TRANSFORMER

+

H.V.

HV SCR

CAPACITOR BANK (30F, 15KV)

LV SCR

Modified Anode The top of the anode is modified in such a manner that the disc (pellet) of the material to be deposited on the substrate just fits in the inner diameter of the anode. The material to be deposited is prepared : by cutting the material in the form of disc and is fitted at the top of the anode by making a disc (pellet) of powdered material in the desired stoichiometry and baking it in a furnace.

A) Breakdown and inverse pinch phase

B) Axial acceleration or rundown phase

C) Radial collapse or focused phase Hot Dense Plasma

D) Post Collapse Phase Highly energetic high fluence ions

Modified Anode and Substrate arrangement for different applications First Few Shots Substrates – Quartz, Si, etc.

Movable Brass Holder

Shutter Hot Dense Plasma

Anode

Material of which nanoparticles are to deposited

Deposition of Nanoparticles of Material on Substrate Substrates – Quartz, Si, etc.

Movable Brass Holder

Hot Dense Plasma Anode

Material of which nanoparticles are to deposited

Shutter

Nanoparticles and Nanostructures have been prepared by optimizing  the distance between the anode and the substrate  the pressure of the gas in the plasma chamber  the charging voltage applied to the capacitor and  the number of shots. ♣ The DPF device has been used to make nanoparticles and nanostructures of different materials

High Resolution Transmission Electron Micrographs

Fullerene size of nanoparticles is of the order of 0.7 nm Chhaya R. Kant, M. P. Srivastava and R. S. Rawat [Physics Letters A 239, 1998, 109]

 PZT average size of nanoparticles is of the order of 0.5 nm Gupta R, Srivastava M P, Balakrishnan V R, Kodama R and Peterson M C [J. Phys. D: Appl. Phys. 37 1091 2004]

AFM images of nanoparticles and nanostructures of different materials produced using dense plasma focus device 1µm

0.5µm

0 µm 0 µm

0.5µm

1µm

Aluminium nanoparticles B D Naorem, S Roy and M P Srivastava [ Journal of Physics: CS 2009 (accepted for publication)

Germanium nanoparticles having diameter in the range of 40-100 nm B D Naorem, S Roy and M P Srivastava [ Submitted in International symposium on applied plasma science 2009]

ZnO nanoparticles having diameter in the range of 40-80 nm in nitrogen ion plasma Yashi Malhotra, Savita Roy and M P Srivastava [ Journal of Physics: Conference series 2009 (accepted for publication)

ZnO nanoparticles in argon ion plasma Y Malhotra, S Roy, M P Srivastava, C R Kant and K Ostrikov

[ Journal of Physics D: applied Physics 2009 (accepted for publication)

cobalt nanoparticles having size in the range of 40-80 nm W P Singh, S Roy and M P Srivastava [ Journal of Plasma fusion and research 2009}

Nickel nanotubes W P Singh, S Roy and M P Srivastava

Collaborators in this work Teachers colleagues from D.U •Savita Roy •Chhaya Ravi Kant •Priti Agarwal •Ruby Gupta

Ph.D Students  N.Bilasini Devi Ashish Tyagi W. Priyo K Singh

 Bhavna Vidhani  Yashi Malhotra

THANK YOU