IN SITU (WET)
ENVIRONMENTAL TEM
Wen-An Chiou
Materials Characterization Center (MC2)
and
Department of Chemical Engineering and Materials Science
University of California at Irvine, Irvine, CA 92612-2575
Pan-American Advanced Studies Institute on
Transmission Electron Microscopy in Materials Science
July 21, 2006
ACKNOWLEDGMENTS
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Nihon University, Tokyo, Japan
A. Fukami
A. Ishikawa
H. Konishi
H. Miyata
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Northwestern University, Evanston
Y.-C. Lee
R. C. Mucic
C. A. Mirkin
D. F. Shriver
JEOL, LTD., Tokyo, Japan
K. Fukushima
University of California, Irvine
K. Foo
L. Lai
Naval Research Laboratory, USA
R. H. Bennett
OUTLINE
INTRODUCTION
Electron Microscopy
The Environment
Purposes
Historical Review of EC Research
Types of In-Situ Observation/Research
How to Maintain Original Hydrated State in the EM
Methods of Containing the Liquid Environment
EC TEM
MATERIALS and TEM RESULTS
Inert Fillers
Clay Minerals
DNA/Au Nanoparticles
SUMMARY
INTRODUCTION
Electron Microscopy
- Daily tool in our modern day research
and development
- Routine for many laboratory (e.g.,
hospital, semi-conductor industry
- Used in all scientific and engineering
field research
Particle Size
 The range in size of grain and/or particles is very great.
At the lower end of the scale: may be a component part of an atom
The upper end of the scale: is not fixed.
Scientists always ask what is the grain/particle size?
 Effect of size on various properties of particles/materials
The most outstanding property : surface-to-mass ratio.
stress σ
The utilization of inorganic nano-particles demonstrated improvements of a
large number of physical and mechanical properties (modulus, strength,
thermal expansion coefficient), barrier, flammability resistance etc.
modified
Unmodified
Conventional
Material
Nanocomposits
Strain ε
What is the Real world?
- Are they real in the EM?
- Vacuum Environment
- Sample Preparation
- Artifacts
- Result and Interpretation
- Understanding of instrumentation & science
The Environment
• Earth, an unique place in the solar system.
- is probably the only planet has water and life, though scientists have
been searching for other possible life in the universe.
• All kinds of LIFE do need H2O,
Our daily life needs water: food, farming, cement, …….
• However, a few things do not like water. For examples:
Electron – Does Not Like H2O, so as electron Microscope
• So we all have to dehydrate our samples before we insert our samples in
to the EM.
• Dehydration – Undesirable Structural and Morphological
modification
How to See the Real World?
In Situ – Examining materials at the original
state/environment.
– the first step for
Dynamic Experiments (in an electron microscope) –
provide a unique and powerful method of studying
materials, especially the response/reaction of materials to
the change of the environment to understand the
fundamental mechanism of any chemical interaction.
e. g., Chemical reaction at elevated temperatures
Gas – solid interaction
Liquid – solid interaction
Liquid – liquid interaction
Type of In Situ Observation/Research
1.
In Situ Deformation
2.
In Situ High Temperature Microscopy
3.
In Situ Low Temperature Microscopy
4.
In Situ Studies of Gas – Solid Interaction
5.
In Situ Environmental (Wet) Cell Microscopy
6.
In Situ Studies of Vapor Deposition
Purposes
1. To introduce the (wet) environmental (cell, EC)
transmission electron microscopy (TEM)
2. To show some research results obtained from
EC TEM
3. To share my thoughts with you and to listen
your ideas and comments
Historical Review of Environmental Cell Research
Since 1935 Marton tried to examine biological materials in hydrated
state….
1944 Abrams and McBain constructed the first enclosed wet cell
Only a very few researchers carried out EC research in the past.
The main reasons:
1. Difficulties on instrumentation.
2. Difficulties on resolution
3. Funding
Between mid-60 through late 70 probably have the most activities.
•
However, it has attracted much attention in the EC TEM research
in the last 3-5 years though they were only limited to EGC TEM
research.
Europe:
Stoyanova, I. G., in Russia (late 1950 to early 1960) on biological
sciences (gas and wet cell), first to examine wet biological
materials in TEM
Heide, H. G., in Germany (early 1960) on Siemens Elmiskope,
biological science (gas controlled environment)
Escaig, J., and Sella, C., in France (mid-1960 to early 1970) on
physical sciences (gas-solid)
Dupoy, G., in France (early – late 1960) on physical sciences (wet
cell)
Swan, P., and Tighe, N. J., in England (during 1970) on physical
sciences (more on gas-solid interaction)
Flower, H. M., (mid 1970) on materials science (gas-solid
interaction, corrosion)
Gai, P. L., (late 1970 to present) in England and in US (after mid1980) on materials science (gas-solid interaction, chemical reaction,
catalysts).
USA:
Allison, D. L. (early to mid 1970) on physical sciences
Hui, S. W., (during 1970 to early 1980) on biological sciences
Moretz, R. C. (late 1960 to early 1970) on biological sciences ,
Parsons, D. F., (early to late 1970) on physical aspect of biological samples.
Gai and Boyes, Du Pont Research (after 1980) on materials aspect, most work
on catalyst research (gas interaction).
ASU group (after early 1990) on the materials science aspect, recent work
concentrated on catalyst research (gas interaction).
Japan:
Ito, T (late 1950) on physical sciences/Instrumentation (gas interaction)
Hashimoto, H., (late 1950 through early 1970), on physical sciences (gas
interaction)
Fukami, A., (late 1960 through late 1980) on physical and biological sciences
and instrumentation (liquid wet cell, liquid-liquid interaction)
Three individual groups, Doi, M, Fujita, H., Nagata, F., and Sakata, S., (early
to mid-1970) on instrumentation and HVTEM
How to maintain the ORIGINAL
(HYDRATED) STATE in the EM?
Principle: The phase-temperature phase diagram for water indicates
that true “wet” conditions only exist at pressures of at least 600 Pa at 0
oC (4.6 Torr = 4.6 mm Hg). In the range 650 to 1300 Pa (5 –10 Torr) the
specimen may be observed while at equilibrium with water.
SEM – Environmental SEM (ESEM),Variable Pressure SEM (1-270 Pa)
– Natural SEM, Partially hydrated – SEM operates at 50 – 90 Pa
TEM- 1. Gas
2. Wet Cell (Liquid/Aqueous Environment)
3. Both gas and liquid
Well Cell – A specimen chamber which is capable of controlling the
environment surround the specimen, but the main microscope vacuum
remains undisturbed.
Methods of Containing the Liquid Environment
1. Window Technique
A pair of electron transparent windows can be placed above
and below the specimen.
The specimen and its surrounding gas/liquid is completely sealed off
from the EM column so the pressure/vacuum of the EM remains
constant.
Need sufficient strong (often thicker) window/film to resist the
pressure difference between the cell and EM, but the resolution and
contrast of image were not seriously degraded.
Risk: Damage of window, possibility of contamination to the
microscope or even chemical attack on the microscope.
The only choice for liquid environment and liquid chemical
interaction research.
This technique can achieve maximum pressure in the cell.
2. Aperture-Limited Technique
A pair of single or multiple small-bore aperture can be placed
above and below the specimen.
Use differential pumping technology.
Gas leakage from around the specimen into the column occurs.
Microscope vacuum is controlled by the size of apertures for
differential pumping
A dynamic balance (equilibrium) between:
1. the gas flow into the cell;
2. the leak rate through the cell aperture;
3. differential pumping aperture; and
4. the pumping speed of the microscope
Transmission Electron Microscopy
(used in this research)
(I)
Modified TEM (JEOL 2000FX)
(II)
Specially Constructed Wet Environmental Cell
(EC) (TEM sample holder)
(III) TEM/EC Vacuum Controller
EC -TEM
JEOL JEM-2000 EX TEM with side-entry
EC holder and gas/liquid control system
A large side-entry specimen holder for EC observation:
(A) cover, (B) inner pipes, and (C) sealing block
Detail Diagram of EC Sample Stage
EC TEM Environmental Control System
Diagram of gas-liquid environmental control system for in-situ wet cell TEM
RESULTS (1)
(I) Polymer Electrolytes
• Potential application in electrochemical devices.
• Composed of conventional polymer electrolyte and inert
fillers, provide an avenue to enhance mechanical strength
while maintain ionic conductivity, if the particle sizes of
these inert fillers are sufficient small (< 1um in diameter).
• To determine the morphology/size of inert fillers to further
our understanding of ion transport phenomena in the
composite system.
Material: Surface modified fume silica (7 um)
(a) SiCl4 was used to activate surface silanol (SiOH) group
and generate reactive groups on the surface of fume
silica particles
(b) Sodium isethionate (HOC2H4SO3Na) interacted with
SiCl groups on the surface to produce surface-modified
fume silica particles. Na = 0.4 Wt.%
(c) (i) Dispersed in tetraethylene glycol dimethyl ether
tetraglyme, H3C(OC2H4)4OCH3)
(ii) Dispersed in water
Original fume silica particles (CTEM)
Untreated fume silica particles (HREM)
Morphology of surface-modified silica particles (CTEM)
Surface-modified silica particles (HREM)
Fume silica particles in tetraglyme medium (In-situ EC TEM)
Aggregated silica particles after removal of tetraglyme medium
(In-situ EC-TEM)
Silica particles in water (In-situ EC-TEM)
Silica particles after evaporation of water (In-situ EC-TEM)
Discussion/Summary:
• The difference in morphologies in two medias may
originated from the difference of polarity and the sodium
content.
• Apparently, the sodium cations on the surface produce a
moderate increase in the hydrophilicity of the particles,
therefore, high dispersion was observed in tetraglyme
medium.
• The relatively low loading of Na cations on the silica
surface prevented full dispersion of silica particles.
RESULTS (2)
(II) Clay (Smectite/Montomorillonite) Particles
-
Ubiquitous on the Earth.
Important in our daily life:
geology, petroleum industry; soil and crop sciences,
Materials science/engineering
Filler, polymer/nanoclay composites……………..
- Layered Al silicate, traditionally believed as broad undulating
mosaic sheets, irregular fluffy masses of extremely small
particles, irregular flake-shaped or platy platelets.
- Objective: To study the particle size/shape analysis in H2O.
- Method:
a) Purified (ion exchanged with Na) and size sieved through
certain size (< submicron)
b) Dispersed in de-ionized water
Question: Are They Real in EM?
•
Problems/Difficulties (of examining smetitic clays):
(a) The individual particles can barely be discerned and are too
small to reveal any characteristic outlines.
(b) Estimations of the areal dimensions are difficult because of the
irregularity
(c) Clays love H2O - Disperse in H2O
- Aggregate when they dry
500 nm
500 nm
Aggregated smectite clay particles (CTEM)
Smecitite clay particles in de-ionized water (In-Situ EC-TEM)
Well-dispersed smectite particles in de-ionized water (EC TEM)
Close-up view of dispersed clay particles (EC TEM)
Particle size analysis
30
25
Individual %
20
15
10
5
0
500
400
300
200
100
100
80
60
40
20
50
40
30
20
10
Particle size (nm)
0
Diameter (nm)
10
2
AR1 (Tc = 5nm)
5
1
Ar2 (Tc = 10nm)
Aggregates formed after evaporation of water in EC TEM
EC TEM micrograph depicting small needle-like and rounded
particles rest on the surface of large platelets.
ED of smecitie clay particle (In-Situ TEM)
High magnification EC TEM revealing elongated thin clay laths
Low magnification EC TEM image showing mixed texture of smectite particles.
EC TEM image revealing not completely dispersed clay particles.
Note the spherical/ball-shape aggregates with empty space inside
the aggregates.
Discussion/Summary:
1. Based on EC TEM study it is clear that the morphology of
smectitic clay minerals is not only existed as plate-like
morphology which has traditionally been proposed (and
observed in a conventional TEM).
2.
Instead there are different shapes and sizes. A variety of shape
such as platelets, needle-like, thin lath, disc and/or spherical,
polygon shape, have been observed in EC TEM.
3.
With well-dispersed clay particles, particle size analysis can
be carried out much easier (without any ambiguity in
differentiating particle shape and boundary)
RESULTS (3)
(III)
DNA/Au Nanoparticles
-The assembly of nanometer sized building blocks, DNA/nanoparticle hybrid materials and assemblies might have useful electrical,
optical and structural properties.
Objective: to observe in situ observation of DNA/Au
nanoparticle assembles in liquid media
Material: Citrate-stabilized Au particles, 8 and 31 nm in diameter
Method:
a) 8 nm Au particles were modified with propylthiol-capped
oligonucleotide, 3’HS(CH2)3-O(O-)P(O))-ATG-CTC-AACTCT
b) 31 nm particles were modified with hexlylthiol-capped
oligonucleotide, 3”TAG-GAC-TTA-CGC-O(O)P(O)O(CH2)6SH
c) The assembly strategy for the oligonucleotide-modified
particles was based on the ability of oligonucleotide to link the
particle together.
Binary particles network assembly (CTEM)
DNA/Au nano-particles satellite structure (CTEM)
Dispersed binary particles without linking olignucleotide (CTEM)
EC TEM image showing DNA/Au assembly in more 3-dimensional structure
Dissociation of DNA/Au nano-particles linkages (2) (In-Situ EC-TEM)
Breakdown of DNA/Au particles linkages (1) (In-Situ EC-TEM)
Dispersed Au particles after electron irradiation (In-Situ EC-TEM)
Dynamic movement of Au nano-particles (In-Situ EC-TEM)
indicating the existence of liquid in the EC.
In-Situ TEM image revealing grain aggregation after prolonged
electron irradiation (continuously increasing the temperature in EC)
without oligonucleotide.
Discussion/Summary:
-Melting analysis of the nanoparticle-modified surface showed
that oligonucleotide hybrization, which is responsible for the
linkage of Au nanoparticles, can be destroyed when temp.> 52 oC.
*Dispersion of Au nanoparticles without any specific linkage
or strands:
-Unstable hybridization and dissociation of DNA/AU linkage
due to the increased temperature in EC by electron beam heating;
- Damage of DNA after prolonged electron irradiation
*Grain growth and aggregation without oligonucletide:
-Continuously increasing the temperature in the EC
Salt precipitates after removal of water (In-Situ TEM)
SUMMARY
1.
These experiments have demonstrated the importance of
environmental (EC) TEM that not only allows dynamic
observation but also provides important research
information.
2.
More researches on EC instrumentation are need:
(a) Stage – sample loading
(b) Vacuum control on EC – computerize control
(c) Resolution
(d) Microchemical analysis
3.
With the EC TEM, more research and new discovery is
awaiting us to explore. The EC TEM is a gold mine to
many scientific (physical, biological, and medical) and
engineering researches.
謝謝
Thank You
Muchas Gracias
References
(1)
(2)
(3)
(4)
Information and micrographs presented herewith were taken from
the research results of the following papers:
W.-A. Chiou et. al., In Situ TEM Study of Inert Fillers in Liquid
Environment: Microsc. Microanalysis (Suppl. 2), MSA, 1998.
W.-A. Chiou et. al., In Situ TEM Study of DNA/Gold Nanoparticles
in Liquid environment: Microsc. Microanalysis (Suppl. 2), MSA,
1999.
W.-A. Chiou et al., Fundamental Thickness of Smectitic Clay
Particles, 13th International Clay Conference, Tokyo, Japan, August,
2005.
References cited on the above papers.