s. girshick, u. minnesota aluminum nanoparticle synthesis and coating steven l. girshick university...

S. Girshick, U. Minnesota

Aluminum Nanoparticle Aluminum Nanoparticle Synthesis and CoatingSynthesis and Coating

Steven L. GirshickUniversity of Minnesota


Objectives1. Synthesize Al nanoparticles using

scalable plasma process

3. Coat particles to passivate surfaces

2. Maintain small primary particle size (high specific surface area) for high reactivity


AcknowledgmentsProf. Michael ZachariahDr. Feng LiaoMr. Bin Zhang (PhD student)Mr. Bo Liu (MS student)Prof. Jeff RobertsDr. Ying-Chih Liao


Why use thermal plasma?Why use thermal plasma?Atmospheric-pressure operation

Completely dissociates reactants to elements

High energy density high throughput in small reactor

Chemical flexibility

Continuous not batch process

Environmentally benign

Scalable


2000 K1000 K

Complete dissociation

Nucleation front

Growth & coagulation

5000 KFlow

Diffusion & thermophoresis

Convection

Particle synthesis in a thermal plasmaParticle synthesis in a thermal plasma


Nanoparticle reactorNanoparticle reactor


Plasma torch / nozzle assembly

DC plasma torch

Injection ringNozzle holder


plasma

Large counterflow

plasma

counterflow

Formation of stagnation layer

Small counterflow

Al2O3 tube

counterflow

plasma


Experimental Experimental DiagnosticsDiagnostics

Plasma torchAr/H2 30/0.5

slmI=200 A, ~10

kW

Counter flow Ar, 85

slm

Diagnostics port

53kPa

Injection Ring 4000 K, 88

kPa

Vacuum pump

Nozzle

Ejector

DMA, for size distribution

N2

Vacuum pump

Water cooled substrate, for RBS sample

TEM grid, for TEM and EDS

Filter holder

Sampling probe

-500

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0 200 400 600 800 1000 1200

Effect of the Flowrate of TMA

0

100000

200000

300000

400000

500000

600000

700000

800000

900000

1000000

1 10 100

Diameter (nm)

dN/dLogDp (#/cc)

RBS

TEM EDS

Size distribution

By-pass

Glass beads and AlCl3 powder

Heated Ar100~200

sccm

Pressure gauge

Vacuum

Packed bed

Heating cable

Thermocouple


Particle sampling & measurement

NanoDMA

TSICNC

3010AEjector

N265 PSI

Ejector

N265 PSI

CriticalOrifice

CriticalOrifice

Bypass

TEM GridHolder

Vacuum

Scanning mobility particle sizer (SMPS)

Sampled aerosol

Dilution


Plasma power input 5–10 kW @ 210–250 A

Chamber pressure 400 Torr

Plasma flow ratesargon 30 slmhydrogen 0.5–2.0 slmAlCl3 10–20 sccm

Counterflowargon 85 slm

Operating conditionsOperating conditions


mica

stainlesssteel

water cooling

by-pass

glass beadsand AlCl3powder

preheatedAr

vacuum

permeable stainlesssteel plate

heatingcable

insulation

line heated andinsulated

heated Ar +AlCl3 vapor

injection ring

nozzle port

tapered tube

AlCl3 vapor delivery system

Entire vapor flow passage is kept hot to avoid pre-condensation


107

108

109

1010

10 100

Particle Diameter [nm]

counterflow on

counterflow off

AlCl3 with 200 sccm carrier gas

Counterflow reduces particle size

SMPS measurementsSMPS measurementsWith & w/out counterflowWith & w/out counterflow


105

106

107

108

109

1010

10 100

Particle diameter [nm]

200 sccm

150 sccm

carrier gas = 100 sccm

counterflow off

SMPS measurementsSMPS measurementsEffect of Ar carrier gas flow rateEffect of Ar carrier gas flow rate

Carrier gas AlCl3 flow rate Dp

AlCl3 flow rate 20 sccm


Inlet of SMPS Inlet of SMPS sampling probesampling probe


Particles deposited onto TEM gridsParticles deposited onto TEM grids

Particles are mostly unagglommerated


Particle on TEM gridParticle on TEM grid

TEM EDS

Background from Si3N4 TEM grid is shown in red

AlO


QuickTime™ and aGraphics decompressor

are needed to see this picture.

Particle diameter 125 nm

Oxide layer thickness 2-5 nm

Oxide layer on particleOxide layer on particle


QuickTime™ and aGraphics decompressor

are needed to see this picture.

Lattice fringe spacing = 2.35 0.033 Å

Al (111) = 2.338 Å

Al particle with surface oxide layerAl particle with surface oxide layer

oxide layer

crystalline Al core


Photoinduced CVDPhotoinduced CVD Gas-phase reactants are activated by UV/VUV photons

Excimer lamps are ideal photon source Commercially available Compact, long-life, reliable UV photons can break most chemical bonds Many wavelengths available

e.g., 172 nm (Xe2*), 222 nm (KrCl*)

Increasingly used for CVD of thin films

Not yet used for coating particles

Xe2*


Photoinduced particle coating: tandem DMA experiment

CxHy in

Ar in

Ar in

N2 in

N2 out

U.V. lampXe2

Lens WindowValve

*

Counter flow

Reactor:Particle synthesis

to vacuum

Sampling probe1

Sampling probe2

CPC

DMA1

DMA2

0.0E+00

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

1.2E+05

10 100

Dp (nm)

0.0E+00

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

1.2E+05

10 100

Dp (nm)

monodisperse

shift due to coating


Tandem DMA

UV lamp

Plasma reactor


1x104

1x105

1x106

0 10 20 30 40Particle diameter (nm)

Al particlesUV off

Measured byDMA1

Size-selected by DMA1;measured by DMA2

DMA #1: polydisperse aerosol enters,monodisperse aerosol exits


In absence of Al particles, UV generates C particles

Introduce CHIntroduce CH44 or C or C22HH22, w/o Al particles, w/o Al particles

0

2000

4000

6000

8000

10000

1 10 100Particle diameter (nm)

UV onNo Al particles

Background0.1 sccm CH4

0.5 sccm CH4

0.1 sccm C2H2

0.5 sccm C2H2


1x102

1x103

1x104

1x105

0 10 20 30 40 50Particle diameter (nm)

Al particles at71:20; UV off

Al + CH4UV on

Al + CH4UV off

Al particles at82:51; UV off

Al particles + CHAl particles + CH44 + UV + UV


0

1x104

2x104

0 10 20 30 40 50Particle diameter (nm)

Al + CH4UV on

Al particles at82:51; UV off Shift in peak due to

surface growth?

First evidence of UV-induced growth of thin C film on surface


Modeling particle nucleation & growthModeling particle nucleation & growth

Truhlar: cluster reactivities & free energies

Girshick: nucleation & growth model, implemented in reactor flow & temperature field

Garrick: effects of turbulence

2000 K1000 K

Completedissociation

Nucleation front

Growth &coagulation

5000 KFlow

Diffusion &thermophoresis

Convection

Al + Al Ä Al2Al2 + Al Ä Al3Al3 + Al Ä Al4

M

Ali−1 + Al Ä Ali

nucleation


SummaryDeveloped thermal plasma process and conducted parametric studies of Al nanoparticle production

Characterized oxide coating on particles

Developed process for photoinduced coating of Al particles with passivating layer

In progress: tandem DMA studies. Preliminary results show growth of thin film on particles

In progress: particle nucleation model that utilizes ab initio calculations of Truhlar’s group

s. girshick, u. minnesota aluminum nanoparticle synthesis and coating steven l. girshick university...

Documents

particle slide

minnesota counterflow

minnesota particles

sccm slide

thermal plasma slide

minnesota acknowledgments

minnesota objectives

unagglommerated slide